ὁ ὢν εἰς τὸν κόλπον τοῦ πατρός

Says ὁ ὤν (ho ōn, "the one who is") is a present participle used attributively of μονογενὴς θεός. εἰς τὸν κόλπον (eis ton kolpon) literally means "into the bosom." In Koine, however, εἰς often stands where ἐν would be expected after verbs of being, so a static "in/at the bosom" (BSB "at the Father's side") is grammatically sound. Motion "toward" should not be pressed.

Says κόλπος ("bosom, chest, lap") pictures closeness and honor at a meal, where guests reclined. The beloved disciple reclines ἐν τῷ κόλπῳ τοῦ Ἰησοῦ (13:23), and Lazarus is in Abraham's κόλπος (Luke 16:22–23).

Implies The phrase forms an inclusio with 1:1b (πρὸς τὸν θεόν). The prologue begins and ends with the Son's intimate relationship with the Father. The beloved disciple's place in 13:23 may mirror it, so the one closest to Jesus bears witness, as the Son, closest to the Father, makes him known.

Uncertain - Whether the present ὤν is timeless ("who is eternally at the Father's side") or written from after the ascension ("who is now at the Father's side"). - Whether ὁ ὤν echoes Exod 3:14 LXX (ἐγώ εἰμι ὁ ὤν). It is possible, but the participle is common, so the team does not build on it.