Paul’s great passion in life was to “know Christ” more and more. He expressed that clearly in Chapter 3 of the book of Philippians. He said that he was “pressing on” to know Christ better and to become more like Him in 
his day to day life. Knowing Christ is the key to spiritual growth. Even after 30 years of knowing Christ, Paul says he does not believe he has arrived at this goal of full knowledge of Jesus or that he has attained a moral perfection in himself. He still had much to learn and far to go to become like Christ. Peter echoes these same truths in 2 Peter 3:18 when he exhorts us to “Grow in the grace and knowledge of our Lord Jesus Christ.” In Philippians 3:15-16 Paul talks to those Christians who understand the need to grow in their knowledge of Christ and who understand that maturity is a process that will never be fully completed until Jesus returns and issues the “upward call” into His presence. It’s only then, when we see Him as He truly is, that we’ll become like Him.
These two verses say, “Let those of us who are mature think this way, and if in anything you think otherwise, God will reveal that also to you.” I see the point of this exhortation is to live our lives in view of the inevitable “upward call” that Paul talked about in Philippians 3:14. If this is a correct observation (which I think it is) then Richison is right when he says, “A good indication whether we are mature in Christ is our orientation to the upward-call. The upward-call is the life orientation towards living for and meeting our Lord.” He then asks his readers, “Are you mature in your life-orientation?”
The final phrase is also important. It concludes, “Only let us hold true to what we have attained.” According to my old New Testament Theology Professor, the late Harold Hoehner, “Quite literally, this expression means ‘to keep step with the same’—as in military marching. In context it means that Christians should keep following those things that effectively work in their lives to promote spiritual transformation.” There are all kinds of things to separate believers into various camps and to cause division in the church. But Paul believes if we’re all marching on, in step, towards increased knowledge of who Jesus is and what He did for us, we’ll find love, peace, joy and the other fruits of the spirit working in our midst. We’ll be united in love as we grow together in our pursuit of a deeper understanding of the Grace of our Lord Jesus Christ. It’s as simple as keeping our eyes on Jesus! Then, marching on together toward Him!