Therefore, just as you have received Christ Jesus as Lord, continue to walk in Him, rooted and built up in Him, established in the faith as you were taught, and overflowing with thankfulness (Col. 2:6-7).
There's an old hymn by William Bradbury based on Jesus' words in Matt. 7:24-27. In the chorus Christians sing:
On Christ, the solid Rock, I stand;
All other ground is sinking sand,
All other ground is sinking sand.
It's a simple principle, but forgotten all too often. In Christ are hidden all the treasures of wisdom and knowledge...(Col. 2:3), and the Colossians were led away from this basic teaching: If you are in Christ, you have found everything (Eph. 1:3). There is an endless supply of wisdom and knowledge, and no end to the spiritual blessings that flow from the knowledge of Christ and applying it in your life.
This is why Paul says, "...rooted and built up IN HIM..." (Col. 2:7). Every other alternative upon which you build your hopes, every other solution offered to you to escape from sin s really no solution. It is counterfeit. It is sinking sand.
The Colossians were in danger. Men had come into their midst with highfalutin, fin-sounding words and Christians were eating it up, thus their faith suffered. The whole reason Paul points this church back to Christ was, as he said, "I say this so that no one will deceive you with persuasive arguments" (Col. 2:4). If you would know your place in this world, your purpose in life, the eternal destiny God intends for you to have--all of these are found in Christ. If you would have real peace, joy, comfort, forgiveness--all of these are found in Christ. There's no need to look to the wisdom to answer these questions. No one except Him can tell you how to have a happy, productive marriage, or raise godly children, or be the most effective boss or employee, or how to deal with difficult people, or how honor your parents.
Trees do not stand strong and withstand the elements because they produce much fruit or have numerous branches, but because they have deep roots. To be rooted or grounded in Christ is to be rooted in His Word--His teachings: "Therefore I will always remind you of these things, even though you know them and are established in the truth you now have" (2 Pet. 1:12).