Christ is the one through whom God reconciles all things; he is the agent or mediator; hence, reconciliation is also attributed to Christ:
And that he might reconcile both in one body to God through the cross, having slain the enmity in it (evn auvtw/|) … Eph 2:16 (KJV)
The ‘both’ (avmfo,teroj) that are reconciled are Jew and Gentile –
“For he is our peace, who has made us both one” (Eph 2:14) and “for through him we both have access in one Spirit to the Father” (Eph 2:18).
The ‘peace’ that is made through the blood of the cross (Col 1:20) is the ‘peace’ between Jew and Gentile –
“by abolishing in his flesh the law of commandments and ordinances, that he might create in himself one new man in place of the two, so making peace” (Eph 2:15).
Paul continues this thought in Colossians,
And you, who once were alienated and enemies in the mind, in evil deeds, he has now reconciled in the body of his flesh by his death, in order to present you holy and blameless and irreproachable before him… Col 1:21-22 (RSV revised)
Here, Paul is addressing the Gentiles at Colossae (Col 1:27) who were once alienated (avpallotrio,w, Eph 2:12, ‘aliens from the commonwealth of Israel’). The reconciling work of Christ presents Gentiles ‘holy’ (cf. Eph 5:27) and the allusion is to Exod 19:6, “and you shall be to me a kingdom of priests and a holy nation.” They were being incorporated into Israel by virtue of being created in Christ.