Unforgiveness

Mat 6:14-15 For if ye forgive mentheir trespasses, your heavenly Father will also forgive you: But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.<

Unforgiveness can result in you losing your salvation if it is not repented of

Offences against others

Mat 5:23-24 Therefore if thou bring thy gift to the altar, and there rememberest that thy brother hath ought against thee; Leave there thy gift before the altar, and go thy way; first be reconciled to thy brother, and then come and offer thy gift.