As far as human achievements are concerned Paul has been there and done that. He excelled beyond others of his own age. But when he met Christ, he found that the righteousness that he received from Christ exceeded whatever righteousness he had up to that point: "But whatever gain I had, I counted as loss for the sake of Christ. Indeed, I count everything as loss because of the surpassing worth of knowing Christ Jesus my Lord. For his sake I have suffered the loss of all things and count them as rubbish, in order that I may gain Christ" (Phil. 3:7-8). NET translates the word "rubbish" (Greek: skubalon) as "dung". So far as Paul was concerned, all his earthly achievements before he knew Christ were as valuable as fecal material.
When compared with the righteousness he now experiences as result of knowing Christ, a righteousness that "comes through faith in Christ, the righteousness from God that depends on faith" he could only use the word "dung" to describe what he formerly had--viz., righteousness based on works, not faith. The righteousness that Paul experienced is not just a faith position but real possession, He didn't strive to produce this righteousness. It was imparted to him because of his faith. In other words, his righteousness was not a reward of his self-discipline but a gift from Christ.
But he admits though he now possesses the righteousness of Chrst, he is not yet perfect. Nevertheless, he is constantly striving to own personally what he has received positionally: "Not that I have already obtained this or am already perfect, but I press on to make it my own, because Christ Jesus has made me his own" (Phil 3:12). So while the righteousness is Christ's, he presses on to make it his own personal possession.
So, Paul was not content with just having the righteousness of Christ as his position (imputed) but as his possession (actual). The key to translate positional righteousness into possessional righteousness is faith.
POSSESSION = POSITION + FAITH
If we believe we have Christ's righteousness as a result of our position in Christ, we can then "press on" to make that righteousness our possession. It's like having a bank account in heaven: positionally, all the money is ours. But we must draw the money out to make it our possession.
So, we mustn't be satisfied with Christ's righteousness that is ours by position. We must make Christ's righteousness our possesssion. That is our goal: "But one thing I do: forgetting what lies behind and straining forward to what lies ahead, I press on toward the goal for the prize of the upward call of God in Christ Jesus" (Phil 3:13-14).
Father, help us translate the righteousness we have by virtue of our position in Christ to become righteousness that we have in our possession from Christ. Amen.