Pay close attention to Jesus’ words in Luke 16:16 – “The law and the prophets were until John. Since that time the kingdom of God has been preached, and everyone is pressing into it.” His statement effectively “time stamps” the beginning point of new testament teaching.
Since about 1970, a few preachers have loudly contended that the books of Matthew, Mark, Luke, and John – along with the first chapter of Acts – ought to be considered part of the old testament, because these books record events that occurred before the “opening day” of the church in Acts 2. Their reasoning would make nearly everything Jesus said while on earth a part of old testament teaching rather than part of the gospel.
The practical effect of their claim – and, it seems, their main purpose – is to make Jesus’ words about divorce and remarriage in Matthew 5 & 19, Mark 10, and Luke 16 “part of the OLD testament” (and therefore – they claim – “not applicable to us today”). Their reasoning completely unravels, however, when we realize that it would also move our Lord’s instructions about salvation (e.g., Luke 13:3 & 5; Matthew 10:32-33; and Mark 16:16) into the era of the old testament. Claiming that Jesus’ words applied only to those who were living under Moses’ law (rather than to all people) is tantamount to saying that they applied ONLY to the Jews of that era, and thus carry no more “weight” of authority for Christians than any other portion of the old testament!
In the context of Luke 16:16, Jesus makes a clear distinction between the old testament (the “Law and the Prophets” – which included John the baptist), and His own message and presence in the world, which pertained to and heralded the establishment of His kingdom. The only logical way Jesus could give the instructions of the gospel was to do so before it actually came into effect; the fact that He did it while Moses’ covenant was still in force in no way diminishes the authority of His words as part of the new testament.