Adam Clarke on 1 Corinthians 15:3

For I delivered unto you first of all - Εν προτοις· As the chief things, or matters of the greatest importance; fundamental truths.

That which I - received - By revelations from God himself, and not from man.

That Christ died for our sins - The death of Jesus Christ, as a vicarious sacrifice for sin, is εν πρωτοις; among the things that are of chief importance, and is essential to the Gospel scheme of salvation.

According to the Scriptures - It is not said any where in the Scriptures, in express terms, that Christ should rise on the third day; but it is fully implied in his types, as in the case of Jonah, who came out of the belly of the fish on the third day; but particularly in the case of Isaac, who was a very expressive type of Christ; for, as his being brought to the Mount Moriah, bound and laid on the wood, in order to be sacrificed, pointed out the death of Christ; so his being brought alive on the third day from the mount was a figure of Christ's resurrection. Bishop Pearce and others refer to Mat 12:40; Mat 16:21; and Luk 9:22; "which two Gospels, having been written at the time when Paul wrote this epistle, were properly called by the name of the Sacred Scriptures." It might be so; but I do not know of one proof in the New Testament where its writings, or any part of them, are called the Scriptures.