Phil. 1:8 For God is my witness how I long after you all in the inward parts of Christ Jesus.
Paul was one with Christ even in the bowels, the tender inward parts of Christ, in longing after the saints. This indicates that Paul did not keep his own inwards but took Christ’s inwards as his. He took not only Christ’s mind but also His entire inward being. Paul’s inner being, therefore, was changed, rearranged, remodeled, reconstituted. His inner being was reconstituted with the inwards of Christ. Paul did not live a life in his natural inner being; he lived a life in the inwards of Christ. (Life-study of Leviticus, p. 85)
Philippians 1:8 indicates that Paul experienced the inward parts of Christ. The Greek word rendered inward parts means “bowels.” It signifies inward affection, then tender mercy and sympathy.
Paul partook of grace, for he longed after all the saints in the inward parts of Christ. To enjoy Christ is to be one in Christ’s inward parts. This refers not only to enjoyment, but also to living Christ. To live Christ is to abide in His inward parts and there to enjoy Him as grace.
Experientially, to magnify Christ and to live Christ require that we remain in the inward parts of Christ. In simple words, this is to abide in Him. If we would be those in Christ, we must be in His inward parts. We need to be in His tender heart and delicate feelings. If we abide here, we shall enjoy Christ as grace and experience Him in a very practical way. (Life-study of Philippians, pp. 29-30)
Further reading: recommending the footnote on Phil. 1:8 in the Recovery Version Bible.
