It belonged not to them, but to us Christians. They only foretold it.
In the general sense, this is the same as what Christ once said to the Apostles: “Many prophets and righteous men desired to see what you see, and did not see it, and to hear what you hear, and did not hear it” (Mt 13:17).
“The things now preached to you” means the whole content of the Gospel, which has disclosed the mystery of human salvation in Christ.
This mystery has only now been preached to you, not earlier, not in the times of the prophets, who only foretold it. Only now has its revelation been accomplished.
To the prophets it was revealed only that this served not themselves, but us.
“By those who preached the Gospel through the Holy Spirit” means those who brought and preached to you the Gospel of Christ by the prompting and inspiration of the Holy Spirit.
As the prophets foretold Christian grace by the Holy Spirit, so the New Testament evangelists preached by the same Spirit, according to Christ’s promise (Jn 14:16-17; 15:26-27; 16:12-15 and parallels).
The word “those who preached the Gospel” does not exclude Peter himself from the number of these evangelists to the readers of the epistle.
This is also confirmed by tradition. It only shows that he was not the only one who preached to them, but that other Apostles did also, especially Paul, as Acts and Church tradition testify.
“Sent from heaven.” This occurred in an especially striking manner on the day of Pentecost (Acts 2), of which some of the readers could have been witnesses.
He was sent from God the Father (Jn 14:16-17 and parallels) and from the Lord Jesus Christ (Acts 2:33; cf. the magnification for the feast of Pentecost).
“Into which,” that is, into what was preached to you, or more precisely, into the content of this preaching, the mystery of human salvation in Christ, angels desire to look.
The Greek word translated “look into” means the attentive examination of something by bending down and pondering it.
The mystery of the salvation of the world revealed in Christ contains such a depth of the riches, wisdom, and knowledge of God (Rom 11:33), that it is an inexhaustible object of contemplation and inquiry even for the most perfect heavenly spirits (Eph 3:10).