Peter is addressing the elders among you
(the leadership-giving men among his readers) because of the fiery trial
(suffering) that invariably will come upon these readers (1 Peter 4:12–19). Peter wants his readers to know that he is addressing them not from an ivory tower free from all (potential) suffering, but as one who knows very well what suffering is.
The phrase witness of the sufferings of Christ
contains two angles:
Peter has himself seen how Christ suffered. He witnessed, for example, how the tide of public opinion turned against Jesus, how the Jewish leaders rejected him, how he agonized in the Garden of Gethsemane, and how he was betrayed, arrested, scourged, and crucified. This speaks to the plural of the word
sufferings.
Peter also experienced personal suffering as a result of belonging to Jesus (John 15:20; John 16:2; Acts 4:3; Acts 5:18, Acts 5:33, Acts 5:40; Acts 12:3–5). The
fiery trial
Peter mentioned in 1 Peter 4:12 will not pass Peter himself by (in whatever forms that may take); in fact, church history records that he eventually died a martyr’s death.
As Peter’s formulation allows for both understandings, we need to hear both nuances in what he is saying to the elders.
1 So I exhort the elders among you, as a fellow elder and a witness of the sufferings of Christ, as well as a partaker in the glory that is going to be revealed: