Paul uses the phrase "being knit together" in love. When Christians quarrel with each other, we know that this is not from God's Holy Spirit which indwells every true believer. One must look deeper and recognize that disagreements can happen but learning to love one another through it is possible with the power of the Spirit which lives in us.
Another phrase Paul uses is: "the mystery of God the Father and of Christ." When I find myself reading a modern day mystery, I am tempted to flip to the back of the book to unveil and discover what happens in the end....to reveal what the mystery is! The whole Bible is in essence a mystery. The Old Testament reveals that there is some mysterious Person beginning with someone called the 'seed of the woman' yet throughout the Old Testament is never named. It isn't until we get to the New Testament that we find out that Jesus is that 'seed of the woman.' We could liken this to the familiar Paul Harvey phrase: "and now for the rest of the story." We discover in the book of Revelation that the mystery of eternity is finally revealed. Go ahead and read it, you will be blessed if you do.
Christ is the One in whom are hid all the treasures of wisdom and knowledge. We need to be treasure hunters. The phrase "to now walk in Christ" means that we have had a change in our inner man. We are now new creatures in Christ and the old pull of the worldly pleasures no longer distracts us like they once used to. To be 'rooted' means that we are grounded or planted deep in the Word of Truth. A plant with shallow roots can't stand the drying winds or the storms of life without dying. Maturity comes in stages, but it must come or we would only be like the seed that was thrown on the rocky ground in Matthew 13:20-21.