A new era began with John the baptizer. Jesus said,
The Law and the Prophets were until John; since then the good news of the kingdom of God has been proclaimed (Luke 16:18; HCSB).
The Old Testament era, otherwise called the period of the Law and the Prophets (as here), had come to an end. As the writer to the Hebrews said,
By saying, a new covenant, He declared that the first is old. And what is old and aging is about to disappear (Hebrews 8:13 HCSB).
These, in similar words, make it plain that we live in a time very different from that of our Lord Jesus. He, and John, lived under the law and were subject to all of its ordinances. Now, however, the old, typical, sacrificial system was over. God even dispensed with the temple itself so that there could be no more of it. By one sacrifice, made once for all for the elect, Jesus Christ died in the place of those whose sins would be forgiven and who would live with Him forever. It is wrong, therefore, to attempt to continue—or insist that others continue—an aspect of that which was fulfilled in the coming of the Lord Jesus.
Nevertheless, there have always those who insist on following dietary laws out of the Law and the Prophets, those who wish to keep fests and festivals, and those who would separate Jewish Christian congregations from mixed ones that Paul clearly identified as altogether new—so much new that they were like a new person as well (See Ephesians 2:15ff).
All tendencies to continue—or bring back the old—is an insult to the Savior Who, instead, came to replace it by His perfect life and death.
The fact that the Law and Prophets were until John means that he had a new message that would by new preaching would produce a new era; let your preaching reflect that fact!