Jamieson, Fausset and Brown on Philippians 2:20

20. His reason for sending Timothy above all others: I have none so "like-minded," literally, "like-souled," with myself as is Timothy. Compare De 13:6, "Thy friend which is as thine own soul" (Psa 55:14). Paul's second self.

naturally--Greek, "genuinely"; "with sincere solicitude." A case wherein the Spirit of God so changed man's nature, that to be natural was with him to be spiritual: the great point to be aimed at. 21. Translate as Greek, "They all" (namely, who are now with me, Php 1:14, 17; Php 4:21: such Demas, then with him, proved to be, Col 4:14; compare 2Ti 4:10; Phm 24).

seek their own--opposed to Paul's precept (Php 2:4; 1Co 10:24, 33; 13:5). This is spoken, by comparison with Timothy; for Php 1:16, 17 implies that some of those with Paul at Rome were genuine Christians, though not so self-sacrificing as Timothy. Few come to the help of the Lord's cause, where ease, fame, and gain have to be sacrificed. Most help only when Christ's gain is compatible with their own (Jud 5:17, 23).