10 Concerning this salvation, the prophets, who spoke of the grace that was to come to you, searched intently and with the greatest care,

Read 1 Peter 1:10 Using Other Translations

Of which salvation the prophets have enquired and searched diligently, who prophesied of the grace that should come unto you:
Concerning this salvation, the prophets who prophesied about the grace that was to be yours searched and inquired carefully,
This salvation was something even the prophets wanted to know more about when they prophesied about this gracious salvation prepared for you.