Therefore, as you received Christ Jesus the Lord, so walk in him, rooted and built up in him and established in the faith, just as you were taught, abounding in thanksgiving.
This seemingly neutral word, “therefore,” can become an important key to good Bible reading and study. I heard someone once say, “when you see the word ‘therefore’ in the Bible, stop and observe what it is there for!” That’s more than just a play on words.
The term is a connection word, connecting what it introduces with previous context. A series of arguments or affirmations are made – then a conclusion is stated.
In this case, Paul has stated [in verses 1-5 of this chapter: (1) Christians need to encourage one another, (2) be knit together in love, (3) seek the full assurance of knowledge, (4) recognize that in Christ there is the fullness of wisdom and knowledge, (5) do not be deluded with plausible arguments, and (6) maintain the firmness of your faith.
So, what does this mean in personal, practical terms? THEREFORE – just as you received Christ Jesus the Lord, so WALK IN HIM.
The Bible here speaks of receiving Christ Jesus the Lord. It is appropriate for us today to speak of receiving Christ Jesus the Lord. In fact, we should be inclined to teach people from the Bible, to do what the Bible says that constitutes receiving Christ Jesus the Lord. It should never become just a phrase we use that has no specific definition. It means exactly what the Bible says it means.
The book of Acts enlightens us. When a sinner understands his/her guilt (Example: Acts 2:23), believes in Christ (Acts 2:36, 8:37), repent and submits to baptism (Acts 2:38), that person has received Jesus Christ the Lord – not just to be forgiven and taken out of sin to God; but to live with Him as the Lord of daily life.
Receiving Jesus Christ as Lord means – you leave sin and start obeying Him. Then à Walk in Him. “Therefore, as you received Christ Jesus the Lord, so walk in Him.” Read again what Paul wrote in the first five verses of the chapter. If those things are true, those who have received Jesus Christ as their Lord should get up every day and walk in Him.
This walk – this way of thinking and living – will bring divine strength into your life. You will discover – as you walk in Him – that you are “rooted and built up in Him and established in the faith, just as you were taught, abounding in thankgiving.”
From the Baker New Testament Commentary Series
6, 7. In close connection with the preceding sentence Paul continues: As therefore you accepted Christ Jesus the Lord, (so) in him continue to live. The chiastic or criss-cross structure of this sentence—with the verbs accepted and continue to live respectively at beginning and end; and the references to Christ, namely, Christ Jesus the Lord and in him, in the center (note forward position of “in him”)—shows that all the emphasis falls on the necessity of clinging to Christ Jesus the Lord (cf. Eph. 3:11; Phil. 2:11), as the all-sufficient One, as the Lord whose commandments should be obeyed and whose word should be trusted. The meaning is, “Colossians, do not be misled. Let your life (your “walk” or conduct) continue to be in harmony with the fact that you have accepted Christ Jesus the Lord as your tradition. You embraced him with a living faith, just as you were taught to do” (see verse 7; cf. Eph. 4:20). The word accepted is here used in its technical sense: received as transmitted (cf. 1 Cor. 11:23; 15:1, 3; Gal. 1:9, 12; Phil. 4:9; 1 Thess. 2:13; 4:1; 2 Thess. 3:6), the line of transmission having been from God to Paul (both directly and indirectly), to Epaphras, to the Colossians.
 Hendriksen, W., & Kistemaker, S. J. (1953-2001). Vol. 6: Exposition of Colossians and Philemon. New Testament Commentary (107). Grand Rapids: Baker Book House.