What did Jesus mean when He said He came to fulfill the Law and the Prophets?
He meant that He had not come to destroy the Law or the Prophets but to fulfill all the covenant promises. He came to bring in the kingdom, government, rule, and reign prepared for Him, proving to Israel that He was the fulfillment of those promises.
Les explains that in Matthew 5:17 Jesus says, "Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfill." Les connects this fulfillment to all the covenant promises, especially the one about the coming kingdom. The nation of Israel had already become a nation and were already in the promised land, but the kingdom, government, rule, and reign had not yet happened. Jesus came to bring in that kingdom and government for which He had been prepared. Earlier context says His miracles and ministry were to prove to Israel that He was the fulfillment, culminating in the resurrection.
Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.