"The law and the prophets were until John: since that time the kingdom of God is preached, and every man presseth into it."
The "law and the prophets" refers to all the writings of the Old Testament. Some who take a superficial view of this text conclude that the whole body of Old Testament Scriptures lost their authority when John began to preach. Nothing could be farther from the truth. Jesus was merely stating that before John's ministry, the "law and the prophets" were all that men had. They constituted man's primary guide to salvation.
Was Jesus implying that those ancient Scriptures would end when the gospel began to be proclaimed? Not at all. The word "until" is used in other passages to show continuing force and application. Refer to Matthew 28:15 and Romans 5:14, where the same Greek word "mechri" is used.
Jesus emphatically affirmed the authority of the Old Testament scriptures, declaring that not a "jot" or "tittle" would be removed. In truth the only Bible available to the first generation New Testament church was the writings of the Old Testament. Believers found their strongest confirmation of faith in it. On one occasion Jesus set forth those writings as sufficient to guide men to heaven (Luke 16:29-31) Paul repeatedly appealed to the law and the prophets in support of his message (Acts 26:22; 28:23).
"Since that time" refers to the time since John began to preach, when additional light had been shining on the pathway of salvation. That new revelation of truth, especially through Christ and His teachings, had brought huge crowds into the way of light and truth. Jesus described it as "every man presseth into it."