Jamieson, Fausset and Brown on 2 Thessalonians 3:16

16. Lord of peace--Jesus Christ. The same title is given to Him as to the Father, "the God of peace" (Ro 15:33; 16:20; 2Co 13:11). An appropriate title in the prayer here, where the harmony of the Christian community was liable to interruption from the "disorderly." The Greek article requires the translation, "Give you the peace" which it is "His to give." "Peace" outward and inward, here and hereafter (Ro 14:17).

always--unbroken, not changing with outward circumstances.

by all means--Greek, "in every way." Most of the oldest manuscripts read, "in every place"; thus he prays for their peace in all times ("always") and places.

Lord be with you all--May He bless you not only with peace, but also with His presence (Mt 28:20). Even the disorderly brethren (compare 2Th 3:15, "a brother") are included in this prayer.