Sam Stein of Huffington Post noted what he thought was a new line in Barack Obama’s victory speech in Houston last night that seemed to designed to tamp down suspicions that he views himself as some kind of messianic political figure. It went:

And I would not be running, as aware as I am of my imperfections, as clear as I am that I am not a perfect vessel, I would not be running if I did not believe that I could lead this country in that new direction, that we have a unique moment that we have to seize.

There is, in fact, nothing new about Obama referring to himself as an imperfect vessel. Over a year ago in Ames, Iowa, for example, he said, “I am not a perfect vessel for your hopes. I can only do this if you do it with me.”
The expression derives from the New Testament, 2 Timothy 2:19-21:

Nevertheless the foundation of God standeth sure, having this seal, The Lord knoweth them that are his. And, Let every one that nameth the name of Christ depart from iniquity. But in a great house there are not only vessels of gold and of silver, but also of wood and of earth; and some to honour, and some to dishonour. If a man therefore purge himself from these, he shall be a vessel unto honour, sanctified, and meet for the master’s use, and prepared unto every good work.

In Catholic thought, the Virgin Mary is not infrequently referred to as a perfect vessel for the messianic being she carried in her womb (see the Immaculate Conception).
Obama’s approach tends to be to portray his mission (so to speak) as something that requires the active participation of his audience. He can only accomplish it “if you do this with me.” This idea of joining together in the upbuilding of society (in preparation for Christ’s return) is classic 19th-century postmillennialism, expressing the optimistic, reformist worldview that once animated the mainline Protestant denomination to which Obama belongs–and which he clearly seeks to reanimate.