Matthew 3:1-2 In those days John the Baptist came preaching in the wilderness of Judea, and saying, Repent, for the kingdom of Heaven is at hand.
The first thing John preached concerning Jesus was repentance.
Luke 13:3 I tell you, No. But unless you repent, you will all likewise perish.
Jesus himself preached repentance and stressed it very strongly.
II Peter 3:9 The Lord is not slow concerning His promise, as some count slowness, but is long-suffering toward us, not purposing that any should perish, but that all should come to repentance.
We find here, about 30 years after the death of our Lord, that repentance was still being preached. Peter shows us that to come to repentance is to avoid perishing; therefore, repentance is necessary to salvation.