Oecumenius
The words I was in the Spirit indicates that he saw a vision which was not perceptible by the senses nor seen with physical ears or eyes, but with prophetic sense.
St. Andrew of Caesarea
"Having mentioned the place and time, St. John indicates likewise his own condition, in which he was vouchsafed the apocalyptic visions. I was in the Spirit on the Lord’s day, he says. In the language of the Prophets, to be in the Spirit is to be in the spiritual condition of a man who sees, hears and feels not only with his bodily organs, but with all his inward being. This is not a dream, for such a condition occurs also when one is awake. In such an extraordinary condition of his spirit, St. John heard a loud voice as of a trumpet.
Apringius of Beja
He says that he was taken up in the spirit, that is, that he was raised up to the secret things which he was to speak. Moreover, he says that he did not enter into the heights of Heaven in a bodily manner, but that he entered in the spirit, recalling this word, “No one has ascended into Heaven except He who has descended, namely the Son of Man, who is in Heaven.(John:13)” The holy apostle Paul also says that he was taken up, but in what way? He says, “Whether in the body or out of the body, I do not know, God knows.(2Cor. 12:2)” He writes that he had been taken up into ecstasy, in the spirit. But since the day of the Lord is mentioned in this passage, when he says that he had been taken up in the spirit, he is indicating that he had been cleansed of any work of a profane kind.
St. Bede
the Lord’s day. He indicates also a fit time for a spiritual vision, for Scripture is wont to express the reason of things in terms, as, frequently, of the place, or the body, or the air, and in like manner, the time. The Angels, namely, visit Abraham at noon(Gen. 18:1), Sodom in the evening(Gen. 3:8); Adam after midday (Gen. 29:1) was afraid at the voice of the Lord, walking up and down; and Solomon received at night(2Chron. 1:2) the wisdom which it was not to be his to retain. heard. He is first admonished by a voice, that he may direct his attention to the vision.
St. John of the Cross
in the spirit: Manifestly, he was transported above the ways of our natural life through the intervention of God. Such substantial visions, even though transitory, occur rarely or hardly ever, and to only a few. For God imparts this kind of vision only to those who were very strong in the spirit of the Church and God’s law. Though these spiritual substances cannot be unclothed and seen clearly in this life by the intellect, they can nonetheless be felt in the substance of the soul by the most delightful touches and conjunctions. (As. Mt Car 24.3-4)
…actually, simply providing spiritual empowerment education to Indigenous Australian children, we did it for 24 hours out of 36 over the weekend, very tiring, but NOTHING removes the veils of our animal nature better than seeing the fruits of ones services to mankind. 
