Jamieson, Fausset and Brown on Colossians 3:24

24. the reward of the inheritance--"Knowing that it is from the Lord (the ultimate source of reward), ye shall receive the compensation (or recompense, which will make ample amends for your having no earthly possession as slaves now) consisting of the inheritance" (a term excluding the notion of meriting it by works: it is all of grace, Ro 4:14; Ga 3:18).

for ye serve--The oldest manuscripts omit "for," then translate as Vulgate, "Serve ye the Lord Christ;" compare Col 3:23, "To the Lord and not unto men" (1Co 7:22, 23).