To be free from intoxication — both literal (not drunk) and metaphorical (mentally alert, self-controlled, spiritually vigilant). The word conveys clearheaded readiness, the opposite of being dulled or stupefied. In NT ethics, nepho is the stance of those awaiting Christ's return.
Paul uses nepho to frame the Christian life as wakeful alertness in contrast to the world's spiritual slumber. 'Let us not sleep, as do others; but let us watch and be sober' (1 Thess 5:6). The imagery is of soldiers on night watch who must stay sharp. Peter ties sobriety to spiritual warfare: 'Be sober (nepsate), be vigilant; because your adversary the devil walks about like a roaring lion' (1 Pet 5:8). The call to sobriety is eschatological — Christ is coming, so stay awake and ready.