The Spirit of Christ who was in them

1 Peter 1:10-12 KJ21
Of this salvation the prophets have inquired and searched diligently, and have prophesied of the grace that should come unto you, [11] searching what, or what manner of time, the Spirit of Christ who was in them had signified when He testified beforehand of the sufferings of Christ and the glory that should follow. [12] Unto them it was revealed that they ministered, not unto themselves, but unto us the things which are now reported unto you by those who have preached the Gospel unto you, with the Holy Ghost sent down from Heaven – things which the angels desire to look into.

I have spent considerable time in the past contemplating just how the Old Testament Saints fit into salvation. Today while briefly thinking about this dilemma, a verse came to mind, 1 Pe 1:11. Which answered the question. Part of the problem that I had in the past was there was really no New Testament scripture I was aware of, that clearly indicated that the Old Testament Saints were in Christ.

Romans 8:9 KJ21
But ye are not in the flesh, but in the Spirit, if so it be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of His.

And I often wondered if having the spirit of Christ was retroactive to the Old Testament Saints? Because the promise to Abraham, that he would be heir of the world was to Abraham and his seed, Ro 4:13, Jesus Christ and those in him.

Galatians 3:14,16,18,29 KJVS
That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith. [16] Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ. [18] For if the inheritance be of the law, it is no more of promise: but God gave it to Abraham by promise. [29] And if ye be Christ’s, then are ye Abraham’s seed, and heirs according to the promise.

So clearly, the Old Testament Saints are in the body of Christ.

1 Peter 1:11 KJVS
Searching what, or what manner of time the Spirit of Christ which was in them did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow.