Acts 13:32-38
In the Old Testament, God promised us an eternal covenant, that is, the sure grace given to David. (Isa 55:3)
Isa 55:3 Incline your ear, and come unto me: hear, and your soul shall live; and I will make an everlasting covenant with you, even the sure mercies of David.
David's sure grace that God promised us in the Old Testament is the resurrection. God raised Jesus from the dead and made Him the first fruits of the resurrection. (Acts 13:32-38)
Acts 13:32 And we declare unto you glad tidings, how that the promise which was made unto the fathers, 33 God hath fulfilled the same unto us their children, in that he hath raised up Jesus again; as it is also written in the second psalm, Thou art my Son, this day have I begotten thee. 34 And as concerning that he raised him up from the dead, now no more to return to corruption, he said on this wise, I will give you the sure mercies of David. 35 Wherefore he saith also in another psalm, Thou shalt not suffer thine Holy One to see corruption. 36 For David, after he had served his own generation by the will of God, fell on sleep, and was laid unto his fathers, and saw corruption: 37 But he, whom God raised again, saw no corruption. 38 Be it known unto you therefore, men and brethren, that through this man is preached unto you the forgiveness of sins:
If we believe in Jesus as the Christ, we too will be resurrected like Christ. (1 Corinthians 15:20-23)
1 Corinthians 15:20 But now is Christ risen from the dead, and become the firstfruits of them that slept. 21 For since by man came death, by man came also the resurrection of the dead. 22 For as in Adam all die, even so in Christ shall all be made alive. 23 But every man in his own order: Christ the firstfruits; afterward they that are Christ's at his coming.