“And be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith:”
King James Version (KJV)
3:9 And be found by God ingrafted in him, not having my own righteousness, which is of the law - That merely outward righteousness prescribed by the law, and performed by my own strength. But that inward righteousness which is through faith - Which can flow from no other fountain. The righteousness which is from God - From his almighty Spirit, not by my own strength, but by faith alone. Here also the apostle is far from speaking of justification only.
Php 3:9 And be found in him. In him "there is no condemnation" (Ro 8:1). Not having mine own righteousness which is of the law. Those in Christ trust not in a legal righteousness, obtained by keeping the law, but that which is through the faith of Christ. But in righteousness which the gospel provides to those who accept Christ through faith. That righteousness is the forgiveness of sins, which is from God by faith. Note that, although the definite article is omitted in our Versions before "faith", the Greek supplies it. "The faith" is equivalent to "the gospel". It is faith in Christ acted upon, causing an acceptance and steadfast obedience to Christ, which secures the righteousness (forgiveness) of which Paul speaks.