Colossians 2:7

rooted and built up in him and established in the faith, just as you were taught, abounding in thanksgiving.

-Colossians 2:7

having been deeply rooted [in Him] and now being continually built up in Him and [becoming increasingly more] established [a]in your faith, just as you were taught, and overflowing in it with gratitude.

-Colossians 2:7 (AMP)

Paul tells us more about what it means to "walk in him".  It means to be "rooted and built up in him".  It means to be "established in the faith".  It means to be "abounding in thanksgiving".  The more I read Colossians the more I am amazed by the centrality of Christ in this book.  We are to be "deeply rooted [in Him] and now being continually built up in Him".  We are given a picture of a plant or tree that has its roots in the ground or soil.  We are to be like that, like a tree with its roots deeply planted into the ground.  We must be deeply rooted in Christ.  From those deep roots into the ground a tree absorbs vital nutrients and grows.  In the same way, we grow from those roots that are gathering vital nutrients from Christ.  The sermon series we're doing at church is called "Rooted" and it's a sermon serious through the book of Colossians.  We are to be rooted in him.  To be rooted in him is what it means to walk in him.