In the prophetic writings in the Old Testament sometimes the day of the Lord is thought of as a day in the near future when God will bring (swift) destruction upon Israel’s enemies (cf. Obadiah 15-16).

But the day of the Lord may also refer to a final, eschatological day of judgment and redemption.

Sometimes a near and a far day of the Lord appear together in the same vision (cf. Isaiah chapter 13: vv. 6-8 (near), vv. 9-11 (far), vv. 17-22 (near))

In the Old Testament the day of Lord will be a day of judgment and wrath (cf. Malachi 4:5) for some but of blessing and salvation (cf. Malachi 4:2) for others.