My witness (μαρτυς μου). Same solemn oath in Romans 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.