Philippians 3:9

Not having mine own righteousness, which is of the law. — This is not the same as “righteousness in the Law,” that is, defined by law. It is a righteousness resulting from the works of the Law (Galatians 2:16), earned by an obedience to the Law, which is “mine own” — “not of grace, but of debt” (Romans 4:4) — such as St. Paul declares (in Romans 10:3) to have been blindly sought by Israel, which he there defines as “life by doing the things of the Law.” We have here, and in the following words, a remarkable link of connection with the earlier Epistles of the Judaising controversy, corresponding to Ephesians 2:8, but cast more nearly in the ancient mould. Yet it is, after all, only the last echo of the old controversy, which we trace so clearly in the Galatian and Roman Epistles. The battle is now virtually won, and it only needs to complete the victory.

But... the righteousness which is of God by (on condition of) faith. — This verse is notable, as describing the true righteousness; first imperfectly, as coming “through faith of Jesus Christ,” a description which discloses to us only its means, and not its origin; next, completely, as “a righteousness coming from God on the sole condition of faith” — faith being here viewed not as the means, but as the condition, of receiving the divine gift (as in Acts 3:16). It may be noted that in the Epistle to the Romans, we have righteousness “through faith,” “from faith,” “of faith;” for there it was needful to bring out in various forms the importance of faith. Here, now that the urgent necessity has passed, we have the stress laid simply on the opposition of the gift of God through Christ to the merit of the works of the Law; and faith occupies a less prominent, though not less indispensable, position. (See Ephesians 2:8, and Note thereon.)