Speaking of the relationship between the atonement and its application, Calvin has this to say:
I have already repeatedly stated, (and it is also easy to prove it from the end of this psalms) that under the figure of David, Christ has been here shadowed forth to us. The apostle, therefore, justly deduces from this, that under and by the name of brethren, the right of fraternal alliance with Christ has been confirmed to us. This, no doubt, to a certain extent belongs to all mankind, but the true enjoyment thereof belongs properly to genuine believers alone. For this reason Christ himself, with his own mouth, limits this title to his disciples, saying,
“Go to my brethren, and say unto them, I ascend unto my Father and your Father, and to my God and your God,”
The ungodly, by means of their unbelief, break off and dissolve that relationship of the flesh, by which he has allied himself to us, and thus render themselves utter strangers to him by their own fault. As David, while he comprehended under the word brethren all the offspring of Abraham, immediately after (verse 23) particularly addresses his discourse to the true worshippers of God; so Christ, while he has broken down “the middle wall of partition” between Jews and Gentiles, and published the blessings of adoption to all nations, and thereby exhibited himself to them as a brother, retains in the degree of brethren none but true believers.
The unbelievers are broken off from Christ by their own fault. That’s worth thinking about.