(1Jn 1:7) The blood of Jesus his Son cleanses us from all sin – OT sacrificial language.
(1Jn 2:2) He is the propitiation for our sins – propitiation for sin is an OT concept.
(1Jn 2:3) Christians are to obey God’s commands.
(1Jn 2:7-8) The command to love is an OT command but now made new as seen in Christ.
(1Jn 2:18) Eschatology – John says this is the last hour.
(1Jn 2:18,22) Eschatology – the antichrist is coming and many antichrists have come have already come. Antichrist denies Christ.
(1Jn 2:28) Eschatology – so that when he appears we may have confidence and not shrink from him in shame at his coming (parousia).
(1Jn 3:2) Eschatology – when he appears we shall be like him, because we shall see him as he is.
(1Jn 3:8) The devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the works of the devil c.f. Gen 3
(1Jn 3:9) Salvation as born of God; as God’s seed abiding in him so that he cannot keep on sinning because he has been born of God.
(1Jn 3:12) We should not be like Cain, who was of the evil one and murdered his brother. And why did he murder him? c.f. Gen 4.
(1Jn 3:22-23) Christians keep his commandments and do what pleases him i.e. believe in the name of his Son Jesus Christ and love one another
(1Jn 4:1) for many false prophets have gone out into the world – same as OT.
(1Jn 4:3) Eschatology – the spirit of the antichrist, which you heard was coming and now is in the world already.
(1Jn 4:10) This is love, not that we have loved God but that he loved us &sent his Son to be the propitiation for our sins – an OT concept.
(1Jn 4:17) Eschatology – We may have confidence for the day of judgment.
(1Jn 5:18) Preservation of the saints – everyone who has been born of God does not keep on sinning but he who was born of God protects him.
(1Jn 5:20-21) Jesus is the true God and eternal life. The command to keep yourselves from idols is very OT-ish.
(2Jn 1:1-2) Election – to the elect lady whom I love in truth because of the truth that abides in us and will be with us forever.
(2Jn 1:5) The command to love is an OT command but now made new as seen in Christ.
(2Jn 1:6) Christians should walk according to his commandments in love.
(2Jn 1:7) Eschatology – Many deceivers have gone out who do not confess coming of Jesus Christ in flesh. Such is the deceiver/antichrist.
(2Jn 1:8) Eschatology – Watch yourselves, so that you may not lose what we have worked for, but may win a full reward.