1 Peter 1:10-11

10 As to this salvation, the prophets who prophesied of the grace that would come to you made careful searches and inquiries, 11 seeking to know what person or time the Spirit of Christ within them was indicating as He predicted the sufferings of Christ and the glories to follow.

The Old Testament Prophets prophesied of the coming Christ and of His grace, yet they had no clear understanding of it—because it was so far in their future. So, they made careful study and inquiries of their own prophetic words in order to understand the Spirit of Christ within them, speaking to them about how He would suffer and then also be glorified (look at Isaiah 52:14-15; 53:1-7; 61:1-3).