The word “therefore” links the command “humble yourselves” to the words of the preceding verse. In the context of the “fiery trial” that would envelop them (1 Peter 4:12), Peter’s readers were to clothe themselves with humility toward each other because “God opposes the proud but gives grace to the humble” (1 Peter 5:5). Since humility is the road to grace, his readers must adopt that posture. In a context of suffering, striving to stand tall and overcome the evil in one's own strength are more tempting attitudes to embrace than humility. So too is an attitude of anger toward God for permitting suffering. Peter would correct such wrong-headed responses.
6 Humble yourselves, therefore, under the mighty hand of God so that at the proper time he may exalt you,