Jesus speaks of how great John the Baptist is and makes the statement that even as great as he is, the lesser (least) in God's Kingdom is greater than he. My question (and one that was asked of me) is, "Are there degrees of acceptance into the Kingdom? How can anyone in the Kingdom be lesser than anyone else?"
The text in Luke says, "greater prophet." This seems to imply that John had a greater measure of knowledge given during his prophetic ministry than any of the previous prophets had. Matthew leaves out the word "prophet," but we must take all of scripture to understand any one given passage. So, we have to understand both Matthew and Luke in terms of the word "prophet."
The least in the kingdom of heaven would be greater than John in that they have greater access to knowledge regarding God's divine will. Remember that the prophets of the old covenant did not have the complete will of God revealed to them. 1 Peter 1:10-12 is helpful in understanding this. The Old Testament prophets prophesied concerning salvation, but did not have the full picture. According to verse 12, even the angels did not have the complete picture of Salvation. It was not until the coming of the Holy Spirit in Acts 2 that "all truth" (John 16:13) was revealed to the apostles and prophets and the "mystery" was unfolded (Romans 16:25,26; Ephesians 3:2-5). John, being the last of the Old Testament prophets, had the greatest knowledge of the plan of Salvation--he KNEW who the Messiah was! However, neither John nor his disciples knew anything about the plan of salvation, the church, the hope of heaven, the resurrection, the indwelling of the Holy Spirit, etc. (see Acts 19:1-6 for comparison). BUT, those who entered the kingdom were taught all of these things before being baptized (Matthew 28:19-21; Acts 8:5, 35). Therefore, the least in the kingdom is greater (in knowledge) than John.
This passage does not teach that there will be greater or lesser (in importance) in the kingdom. Jesus' own disciples were mistaken on this concept as well and he reproved them for it (Matthew 18:1-4; Matthew 20:26-28). Even when Jesus is using this language of the greatest shall be the servant, he is not implying that there will be one that is "greatest." The Bible nowhere teaches that any Christian should expect to be considered greater than any other Christian. This was one of the problems that the church at Corinth had. Paul taught them that all members are equally important even though their function was different (1 Corinthians 12:12ff). God does not respect persons and would never allow for such in His kingdom (Acts 10:34).