For Paul, as for most first-century Jews, the day of YHWH, the judgment of the wicked, and the kingdom of God were inextricably bound together eschatologically. 

Thus, discipleship is contingent upon spiritual focus and sobriety: “Pay careful attention, then, to how you live—not as unwise people but as wise—making the most of the time, because the days are evil” (vv. 15–16, CSB). Because this age is inherently corrupt and evil (cf. Rom. 8:20; Gal. 1:4; Eph. 2:2), it demands a militant attitude (cf. Eph. 6:10–20), so as “to stand against the schemes of the devil” (6:11). Believers ultimately wrestle against “the cosmic powers over this present darkness” (v. 12; emphasis added), which assumes the coming age of light. -John P. Harrigan