1 Peter 1:10

The apostle having described the persons to whom he wrote, and declared to them the excellent advantages they were under, goes on to show them what warrant he had for what he had delivered; and because they were Jews, and had a profound veneration for the Old Testament, he produces the authority of the prophets to convince them that the doctrine of salvation by faith in Jesus Christ was no new doctrine, but the same which the old prophets did enquire and search diligently into. Note, I. Who made this diligent search - the prophets, who were persons inspired by God either to do or to say things extraordinary, above the reach of their own studies and abilities, as foretelling things to come, and revealing the will of God, by the direction of the Holy Spirit. II. The object of their search, which was salvation, and the grace of God which should come unto you; the general salvation of men of all nations by Jesus Christ, and more especially the salvation afforded to the Jews, the grace that should come to them from him who was not sent but to the lost sheep of the house of Israel. They foresaw glorious times of light, grace, and comfort, coming upon the church, which made the prophets and righteous men desire to see and hear the things which came to pass in the days of the gospel. III. The manner of their enquiry: they enquired and searched diligently.

— Matthew Henry's Concise Commentary (public domain)

The magnitude of this "salvation" is proved by the earnestness with which "prophets" and even "angels" searched into it. Even from the beginning of the world this salvation has been testified to by the Holy Spirit. prophets--Though there is no Greek article, yet English Version is right, "the prophets" generally (including all the Old Testament inspired authors), as "the angels" similarly refer to them in general. inquired--perseveringly: so the Greek. Much more is manifested to us than by diligent inquiry and search the prophets attained. Still it is not said, they searched after it, but concerning (so the Greek for "of") it. They were already certain of the redemption being about to come. They did not like us fully see, but they desired to see the one and the same Christ whom we fully see in spirit. "As Simeon was anxiously desiring previously, and tranquil in peace only when he had seen Christ, so all the Old Testament saints saw Christ only hidden, and as it were absent--absent not in power and grace, but inasmuch as He was not yet manifested in the flesh" [CALVIN]. The prophets, as private individuals, had to reflect on the hidden and far-reaching sense of their own prophecies; because their words, as prophets, in their public function, were not so much their own as the Spirit's, speaking by and in them: thus Caiaphas.

— Jamieson-Fausset-Brown Commentary (public domain)