Once a person comes to faith (i.e. believes Jesus is the Christ and Lord), he or she will obey what the Lord says. The Lord has spoken thru the Apostles and Prophets that repentance is required. Repentance is a change of will to stop doing things not acceptable to the Master and to start doing things acceptable to Him.
Here are some ways we learn that Christ requires repentance:
Jews in Jerusalem on Pentecost
Peter & John's Sermon to Jews in Jerusalem
The Lord's Desire
The Kindness of God
What is Repentance?
Merriam Webster Dictionary
Biblical Definition: Change of will to stop sinning
Being sorry for our sins is not repentance but it produces repentance
When my faith in Christ causes me to decide to leave my sin and do whatever He teaches—
What must I actually do to be forgiven of my sins?