In a literal sense, being sober-minded contrasts with being under the influence of alcohol. Peter, however, is using the term in the context of thinking and so the reference is to clear-mindedness in a bigger way than simply the absence of alcohol. The sobriety he is commanding implies that the recipients of God’s grace are not to let anything distract their attention from full concentration on the significance of Christ’s impending return.
7 The end of all things is at hand; therefore be self-controlled and sober-minded for the sake of your prayers.