What is the marriage supper of the Lamb?"
In his vision in Revelation 19:7-10, John saw and heard the heavenly multitudes praising God because the wedding feast of the Lamb—literally the "marriage supper"—was about to begin. The concept of the marriage supper is better understood in light of the wedding customs in the time of Christ.
There were three major parts of these customs. First, a marriage contract was consummated between the parents of the bride and the bridegroom, and the parents of the bride would pay a dowry to the bridegroom or his parents. This was called the betrothal period, what we would today call the engagement. This period was the one Joseph and Mary were in when she was found to be with child (Matthew 1:18; Luke 2:5).
The second step usually occurred a year later, when the bridegroom, accompanied by his male friends, went to the house of the bride at midnight with a torchlight parade through the streets. The bride would know this was going to take place, and so would be ready with her maidens, and they would join the parade that would end up at the bridegroom's home. This was illustrated in the parable of the virgins in Matthew 25:1-13. The third phase was the marriage supper itself, which might go on for days as illustrated by the wedding at Cana in John 2:1-2.
What John’s vision in Revelation pictures is the wedding feast of the Lamb (Jesus Christ) and His bride (the Church) in its third phase, the implication being that the first two phases have already taken place. The first phase was consummated on earth when each individual member of the Church, the body of Christ made up of believers, placed his or her faith and trust in Christ as Savior. The dowry paid to the Bridegroom’s Parent (God the Father) would be the shed blood of Christ on the cross on the Bride’s behalf. Now the Church would belong to Christ in the sense of betrothal and, like the wise virgins in the parable, all would be watching and waiting for the appearance of the Bridegroom (the Second Coming). The second phase symbolizes the Rapture of the Church when Christ comes to claim His bride and take her to the Father's house. The marriage supper then follows as the third and final step.
The wedding feast to which the saints are invited includes not only the Church as the bride of Christ, but others as well. The "others" include Old Testament saints who are going to be raised at the Second Coming, as well as the martyred dead of the Tribulation who form the multitude. As the angel told John to write: “Blessed are those who are invited to the marriage supper of the Lamb” (Revelation 19:9). It is a glorious celebration of all who are in Christ, and since we will be in our spiritual state (bodies), there will be no need for food!