…that I may gain Christ and may be found in Him, not having a righteousness of my own derived from the Law, but that which is through faith in Christ, the righteousness which comes from God on the basis of faith
– Philippians 3:8b-9
Our being found in Christ is actually in three stages. Firstly, we are found in His completed and accomplished work. From the moment we took Christ as our Savior, God declared us righteous, and we have been continually found in Christ. Since this is the case, why would Paul still seek to be found in Christ? It is because there are further stages of being found in Christ.
Adapted from Philippians: That I May Gain Christ by Titus Chu, page 192