Peter reminded his readers that the prophets had predicted that Jesus Christ"s life, as their own lives, would include suffering followed by glory. He mentioned this to encourage them to realize that their experience of suffering for their commitment to follow God faithfully was not abnormal. [source][source][source]
"To the elaborated and elevated declaration of his eschatological vision in 1 Peter 1:6-9, Peter now adds an explanatory postscript in a more didactic style. He pauses to measure the greatness of the salvation mentioned in 1 Peter 1:5; 1 Peter 1:9 with a brief but wide-ranging reflection on the past and present. The curiosity of "prophets" ( 1 Peter 1:10) and "angels" ( 1 Peter 1:12) underscores the mystery of the divine plan: God in his sovereignty has long kept secret the salvation soon to be revealed to his chosen ones (cf. Ephesians 3:4-6)." [1][source]
These verses reveal a chiastic structure centering on the idea that God clarified what had formerly been unclear to the prophets. [source][source][source]