Just in case anybody missed the key line from his homily during Tuesday's inaugural Mass , Pope Francis later made it his third tweet since taking office: "True power is service. The Pope must serve all people, especially the poor, the weak, the vulnerable."
The line builds on a consistent theme since Francis' election, memorably expressed during a meeting with journalists  Saturday.
"How I would like a poor church for the poor," Francis said. It's a fitting sentiment for a pope who took his name from Francis of Assisi, a saint renowned for his love affair with Lady Poverty.
Now that the new pope has reached the end of his beginning, the focus will shift from style to substance, meaning the hard work of translating his promising start into the nuts and bolts of policy. With regard to fostering a "poor church for the poor," Francis will face at least four challenges right out of the gate.
1. The myth and reality of Vatican wealth
Given the magnificence of St. Peter's Basilica and the Apostolic Palace, the Vatican may seem a counterintuitive place to pursue the dream of a poor church. Some may expect the new pope to hold a fire sale in St. Peter's Square -- in a metaphorical sense following his namesake, Francis of Assisi, by stripping the place naked before starting anew.
Such a program is, in truth, easier to applaud than to accomplish.
To begin with, the legendary wealth of the Vatican is to some extent more myth than reality. The Vatican has an annual operating budget of under $300 million, while Harvard University, arguably the Vatican of elite secular opinion, has a budget of $3.7 billion, meaning it's 10 times greater. The Vatican's "patrimony," what other institutions would call an endowment, is around $1 billion. In this case, Harvard's ahead by a robust factor of 30, with an endowment of $30.7 billion.
The Vatican bank controls assets estimated at more than $6 billion, which is nobody's idea of chump change, but most of that isn't the Vatican's money. It belongs to religious orders, dioceses, movements and other Catholic organizations, and is managed by the Institute for the Works of Religion to facilitate moving it around the world.
Of course, these figures don't include the value of masterpieces of Western art housed in the Vatican, such as Michelangelo's "Pietà." The Vatican considers itself custodians of these items, not their owners, and it's a matter of Vatican law that they can never be sold or borrowed against. As a result, they have no practical value and are listed on the Vatican books at a value of 1 euro each.
Aside from selling off the papal limo, which Pope Francis doesn't seem inclined to use, and baubles such as the crimson-lined mozetta, which he doesn't seem inclined to wear, it's hard to see immediately what he could jettison that would dramatically alter perceptions.
Moreover, Francis was elected in part on a platform of overhauling the Vatican's bureaucracy in the direction of greater transparency, accountability and efficiency. Assuming he assembles a team of reformers, he'll need to make sure they have the tools to do the job. At least initially, that might require more money for Vatican operations rather than less.
On the other hand, Paul VI famously decided to retire the papal tiara, or crown, and asked that proceeds from its sale go to the poor. Perhaps Francis can do the same, renouncing a few items associated with the Vatican's regal past as a further step toward modesty.
In any event, it might help matters if the outside world could see the relatively Spartan settings in which most Vatican officials actually live and work as opposed to the resplendent backdrops used to stage public rituals. Simply by lifting some of the veils of secrecy, Francis might move a long way toward recalibrating impressions.
2. Financial transparency
If Francis is serious about preaching a "poor church" to the world, he'll be challenged to make sure the Vatican keeps its own nose clean with regard to money management. In the past, both distant and recent, it's an area where the Vatican sometimes has stumbled.
One of the more spectacular revelations to result from the Vatican leaks crisis were letters written by a former senior official in the government of the Vatican City State, today the pope's ambassador to Washington, D.C., describing widespread corruption and cronyism in Vatican finances. Although the dollar amounts are small by the standards of large organizations, the charges nevertheless gave the Vatican a black eye.
The Vatican bank has also faced persistent charges of shady dealings. Both the president and the director, Italian layman Paolo Cipriani, were placed under investigation by Italian authorities in 2010, and at the same time $30 million in assets were seized for allegedly failing to follow European anti-money-laundering protocols. The money was released in May 2011, and no criminal charges have been filed against the two officials.
Last May, renowned Italian economist Ettore Gotti Tedeschi was ousted as the bank's president following an internal power struggle. He had been appointed in 2009 with the profile of a reformer, but a council of supervisors faulted him for erratic behavior and poor job performance.
Most recently, the Deutsche Bank Italy announced Dec. 31 that it was suspending electronic payment services for the Vatican because it lacked an adequate banking regulatory authority. The Vatican briefly became a cash-only business, unable to accept credit cards at its museums and post office. Those services were restored after the Vatican worked out a new deal with the Swiss cashless payment firm Aduno SA.
Defenders of Benedict XVI argue this is an area in which the former pope profiles as a reformer.
Benedict created a new "Financial Information Authority" in the Vatican, empowering it to inspect the books of other departments. That was a minor cultural revolution, since the various Vatican offices are accustomed to being semi-autonomous fiefdoms accountable only to God and the pope, and in both cases fairly nominally.
Benedict also brought in a renowned anti-money-laundering expert to run the agency, a Swiss lawyer named René Brülhart, whose previous claim to fame is cleaning up Lichtenstein's reputation as a financial pariah. The appointment was read by money laundering experts as a clear signal the Vatican is in earnest.
More stunning still, Benedict OK'd a first-ever evaluation of the Vatican's financial operations by Moneyval, the Council of Europe's anti-money-laundering agency. Never before has the Vatican opened its financial and legal systems to external, independent review, with the results made public. In centuries past, had secular authorities shown up to conduct such an investigation, they would have been fought off tooth and nail. For Moneyval, the red carpet was rolled out instead.
Francis will be challenged to continue those reforms, especially on the two most serious question marks identified in the Moneyval evaluation: the role and powers of the new watchdog agency, and external regulation of the Vatican bank.
If nothing else, Francis may need to press both his financial personnel and his communications experts to do a better job of persuading the outside world that the Vatican is playing by the rules. However clean the place may be on the inside, it will take time, and probably a far stronger dose of sunshine, for external perceptions to catch up.
3. The church and politics
For many people, including many Catholics, concern for the poor is credible only if it comes with a political edge. That was the essence of the liberation theology movement that grew up in Latin America in the 1960s and '70s, which sought to place the church on the side of the poor in the struggle for social change.
Famously, then-Fr. Jorge Mario Bergoglio, at the time serving as Jesuit provincial in Argentina, was not exactly enamored of liberation theology. His reluctance wasn't born of indifference to the poor, but rather a conviction that individual conversion has to precede structural change, and that priests should not lose sight of their primary role as ministers of souls.
Still, many Latin American Catholics at the time read his position as at odds with the interests of social justice, and the whole world might be inclined to draw the same conclusion if Francis continues to insist on keeping the church at arm's length from politics.
Francis obviously believes that the political status quo is unjust, a point driven home for him by Argentina's economic crisis from 1999 to 2002. That experience helped inspire these words during a 2007 session of the Latin American bishops: "We live in the most unequal part of the world, which has grown the most yet reduced misery the least," the future pope said. "The unjust distribution of goods persists, creating a situation of social sin that cries out to Heaven and limits the possibilities of a fuller life for so many of our brothers."
Hearing his talk about a "poor church for the poor," many people will naturally expect Pope Francis to challenge social and political injustices head-on -- pushing for greater financial assistance for the developing world, for instance, or for reform in international institutions such as the World Bank and International Monetary Fund, or demanding that Western governments live up to their obligations under the U.N. Millennium Development Goals.
To the extent that he takes such stances, he'll face blowback from conservative quarters of opinion inside and outside the church, as well as from secular observers who wonder what qualifies a religious leader to pronounce on economic policy. If he shrinks from specific advocacy, critics may be tempted to conclude that all this "church for the poor" rhetoric is hollow.
All popes, of course, face the challenge of working out precisely how "political" they should be, realizing full well that somebody's going to be unhappy no matter what they do. Yet for a pope who comes into office touting concern for the poor as the beating heart of his pontificate, the stakes are especially high.
4. Simplicity vs. security
One way Francis has signaled his concern for the poor and the vulnerable is by making himself available to them as much as possible. During his inaugural Mass on Tuesday, for instance, he insisted on taking an open-air Jeep for his swing through St. Peter's Square rather than the bulletproof popemobile, at one point hopping out to embrace an infirm man.
At the level of symbolism, such behavior projects a lively concern for ordinary people, especially those at the margins, which has captured the imagination of the world, and it may well fuel a deeper spirit of service among the Catholic rank and file.
It is also, however, inspiring heart palpitations among Vatican security personnel, who are deeply concerned that the new pope is leaving himself far too exposed.
For those whose memories reach back this far, the sight of Pope Francis in that Jeep on Tuesday morning may have elicited a flashback to May 13, 1981. This is precisely how John Paul II used to make his way through the square until an assassin's bullet nearly cost him his life, and the popemobile was designed as a compromise between accessibility and safety.
I've said on CNN a few times that the only people not charmed by Francis so far are his security agents, who are being driven nuts. The line always draws a chuckle, but if something were to happen to Francis, it would suddenly be no laughing matter.
Francis is no naïf when it comes to how he's perceived, and he knows it's tough to preach love for the poor if you live completely cut off from them. Popes teach with gestures as much as words, so the image of him embracing ordinary people, sharing their joy and pain, has undeniable iconic value.
At the same time, any pope also has a responsibility not to place unreasonable burdens on the people charged with protecting his safety. That's a balance Francis will have to strike as this "Pope of the Poor" settles into office.
[Follow John Allen on Twitter: @JohnLAllenJr]