Luke 13:2-5 (KJV)

2 And Jesus answering said unto them, Suppose ye that these Galilaeans were sinners above all the Galilaeans, because they suffered such things?

3 I tell you, Nay: but, except ye repent, ye shall all likewise perish.

4 Or those eighteen, upon whom the tower in Siloam fell, and slew them, think ye that they were sinners above all men that dwelt in Jerusalem?

5 I tell you, Nay: but, except ye repent, ye shall all likewise perish.

Repentance is an essential part of the gospel. John the Baptist, Jesus, and the apostles called people to repentance. Jesus Himself said in 
Mark 2:17b (KJV) ….They that are whole have no need of the physician, but they that are sick: I came not to call the righteous, but sinners to repentance.
Repentance is not a once off but we need to repent whenever we realise we missed the mark and sinned Turing away from it.
Revelation 2:5 (KJV) Remember therefore from whence thou art fallen, and repent, and do the first works; or else I will come unto thee quickly, and will remove thy candlestick out of his place, except thou repent.
God’s love and goodness desires everyone to repent.
2 Peter 3:9 (KJV) The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.
Repentance requires humility, a realisation and acknowledgment that we come short and sinned. Pride and love of sin go in the way of repentance.
Let us walk in humility before God and each other and keep short accounts with God turning away from the sin that we committed and turn to God fully trusting the work that Jesus Christ did on the cross for us.