With this phrase Peter indicates that God had his eye specifically on Peter’s readers when he disclosed Jesus Christ. The point, of course, is not that God revealed Jesus Christ only for the sake of Peter’s readers (to the exclusion of other people). Even so, it is certainly encouraging for people who feel displaced (1 Peter 1:1, 1 Peter 1:17) to know that they are so valuable to God that he sent the eternally designated Christ at the time of his choosing to ransom them. The point is equally valid for all “elect exiles” of whatever time or circumstance.
20 He was foreknown before the foundation of the world but was made manifest in the last times for the sake of you