Third Heaven

The meaning of "third heaven" is not entirely clear. Rabbinical sources mention seven heavens, and Paul may have been speaking from this perspective -- perhaps indicating that he had received an incredible revelation, though not the highest. By some accounts, "third" is a temporal referent, the "third heaven" being the one that exists right now, the abode of departed believers.

The cause of this "catching up" was God himself, the giver of revelation. The experience is quite similar to a number of Old Testament prophetic experiences (e.g. Isa. 6). God occasionally gave his prophets and apostles (compare John's Revelation) visions of heaven itself. Also, the Old Testament tabernacle and temple were places where heaven and earth intersected. To be in either of these was to be simultaneously in the heavenly court of God, as in Isaiah 6.

In any event, since Paul's point is the defense of his own apostleship, we can assume that the revelation surpassed anything that the false apostles (2 Cor. 11:13) claimed for themselves. It was an incredible revelation of the heavenly realm, given directly to Paul (in my opinion Paul was speaking of himself) by God, and given especially for Paul himself (at least in content).