Holding God and His will in high regard is the right motive. They are to work heartily (Putting their whole inner man into the effort), as for the Lord rather than for men, serving their master as they would the Lord Himself.
Paul stresses to Timothy that such obedience and honor given by slaves to their masters keeps “the name of God and our doctrine” from being evil spoken of (1 Tim. 6:1).
23 In 3:17 Paul enjoins the Colossians in general to do all things in the name of the Lord Jesus. At the outset of v. 23, the apostle admonishes slaves in particular to work heartily (lit., “from [your] soul”; NIV, “with all your heart”) in whatever they do. Slaves are to not only obey their masters with singularity of heart but are also to perform their given duties with all the energy they can muster. A slave characterized by integrity and productivity would be a valued commodity for any master. That being said, this is not what ought to motivate their work; rather, Paul directs slaves to expend their energies as to the Lord and not their masters, who are, in the final analysis, mere mortals. Even though they work for their lords, they are to do their work for their Lord.
 MacArthur, J. F., Jr. (1992). Colossians (p. 172). Chicago: Moody Press.
 Still, T. D. (2006). Colossians. In T. Longman III & D. E. Garland (Eds.), The Expositor’s Bible Commentary: Ephesians–Philemon (Revised Edition) (Vol. 12, p. 342). Grand Rapids, MI: Zondervan.