John Gill Commentary Philemon 1:12

"whom I have sent back to thee in his own person, that is, my very heart:" — Philemon 1:12 (ASV)

Whom I have sent again
From Rome to Colosse, or to Philemon, wherever he was, along with this epistle:

you therefore receive him, that is, mine own bowels ;
meaning his son, who, in a spiritual sense, came out of his bowels, to whom he stood in the relation of a spiritual father; so the Syriac version renders it, as my son, so receive him; see (Genesis 15:4) (2 Samuel 16:11).

And for whom he had a most strong affection, and tender regard; his bowels yearned for him, and he suggests by this expression, that should he reject him, it would give him the utmost pain and uneasiness; and he should be obliged to cry out as the Prophet Jeremy did, "my bowels, my bowels, I am pained at the very heart"; (Jeremiah 4:19) wherefore he entreats him to receive him again into his house and family, into his service, and into his heart and affections, where the apostle had received him.