II John 1:9 Whosoever transgresseth, and abideth not in the doctrine of Christ,
hath not God. He that abideth in the doctrine of Christ, he hath
both the Father and the Son.
1:10 If there come any unto you, and bring not this doctrine, receive him
not into your house, neither bid him God speed:

Can someone expalin what is the doctrine of Jesus Christ?

the doctrine of Christ is all about faith in the Son of God-Christ Jesus.one in which the righteousness is mainly of faith.

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Igbinoba Bright

Matt 18:21 Then came Peter to him, and said, Lord, how oft shall my brother sin against me, and I forgive him? till seven times?
Matt 18:22 Jesus saith unto him, I say not unto thee, Until seven times: but, Until seventy times seven.
Eph 4:32 And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you.
Matt 6:14 For if ye forgive men their trespasses, your heavenly Father will also forgive you:
Matt 6:15 But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.
Col 3:12 Put on therefore, as the elect of God, holy and beloved, bowels of mercies, kindness, humbleness of mind, meekness, longsuffering;
Col 3:13 Forbearing one another, and forgiving one another, if any man have a quarrel against any: even as Christ forgave you, so also do ye