What were the Old Testament prophets searching for when they wrote their prophecies?
The Old Testament prophets searched diligently to understand the salvation and grace that was to come, and what manner of time the Spirit of Christ in them was signifying when He testified beforehand of Christ's sufferings and the glory that would follow. They wrote by inspiration but could not fully put it all together.
Les explains that in I Peter 1:10-12, Peter writes that the Old Testament prophets, such as Isaiah, Jeremiah, and Ezekiel, inquired and searched diligently concerning the salvation and grace that should come. They prophesied of future things, and the Spirit of Christ within them testified beforehand of the sufferings of Christ and the glory that should follow. They sought to know what manner of time the Spirit was indicating. Les notes they could not put it all together, similar to Daniel, who was told to shut up the book because it was not for him to know, though at the end of time it would be known. The glory spoken of likely refers to His Kingdom, though Christ was also glorified when He defeated Satan at the cross. The prophets wrote by inspiration but did not fully understand the timing or the full picture.
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.