Revelation 1:10

New English Translation

¹⁰I was in the Spirit^[a] on the Lord’s Day^[b] when^[c] I heard behind me a loud voice like a trumpet,

Revelation 1:10 tn Or “in the spirit.” “Spirit” could refer either to the Holy Spirit or the human spirit, but in either case John was in “a state of spiritual exaltation best described as a trance” (R. H. Mounce, Revelation [NICNT], 75).
Revelation 1:10 tn Concerning the phrase κυριακῇ ἡμέρᾳ (kuriakē hēmera) BDAG 576 s.v. κυριακός states: “pert. to belonging to the Lord, the Lord’s…κ. ἡμέρᾳ the Lord’s day (Kephal. I 192, 1; 193, 31…) i.e. certainly Sunday (so in Mod. Gk….) Rv 1:10 (WStott, NTS 12, ’65, 70-75).”
Revelation 1:10 tn The conjunction καί (kai) is not introducing a coordinate thought, but one that is logically subordinate to the main verb ἐγενόμην (egenomēn).

New English Translation (NET)