Now we know that [Christ] is of no avail save only to those to whom he is a head and the first-born among the brethren, to those, in fine, who are clothed with him. To this union alone it is owing that, in regard to us, the Savior has not come in vain. To this is to be referred that sacred marriage, by which we become bone of his bone, and flesh of his flesh, and so one with him (Eph. 5:30)....
Calvin, Institutes, Book 3, 1.3
There is no benefit of salvation to unbelievers.
And further along that line of thinking, Christ only aids to salvation those who are Abraham's seed who are the children of God's promise, so they they are elect of God to be the saved.
Hebrews 2
Bringing Many Sons to Glory
10 For it was fitting for Him,
for whom are all things and by whom are all things, in bringing many sons to glory, to make the captain of their salvation perfect through sufferings. 11 For both He who sanctifies and those who are being sanctified
are all of one, for which reason He is not ashamed to call them brethren, 12 saying:
“I will declare Your name to My brethren;
In the midst of the assembly I will sing praise to You.”
13 And again:
“I will put My trust in Him.”
And again:
“
Here am I and the children whom God has given Me.”
14 Inasmuch then
as the children have partaken of flesh and blood, He Himself likewise shared in the same, that through death He might destroy him who had the power of death, that is, the devil, 15 and release those who through fear of death were all their lifetime subject to bondage. 16 For indeed He does not give aid to angels,
but He does give aid to the seed of Abraham. 17 Therefore, in all things He had to be made like
His brethren, that He might be a merciful and faithful High Priest in things
pertaining to God, to make propitiation for the sins of the people. 18 For in that He Himself has suffered, being tempted, He is able to aid those who are tempted.