A.T. Robertson Commentary Philippians 1:8

"For God is my witness, how I long after you all in the tender mercies of Christ Jesus." — Philippians 1:8 (ASV)

My witness (μαρτυς μου). Same solemn oath in Ro 1:9.

I long after (επιποθω). Longing (ποθος) directed toward (επ) the Philippians. Old word, chiefly in Paul in N.T.

In the tender mercies (εν σπλαγχνοις). Literally "in the bowels" as the seat of the affections.