Notice how the New American Standard Bible renders Luke 3:22,
"And the Holy Spirit descended upon Him in bodily form like a dove."
"Bodily" is "Somatikos" which is defined in the NAS New Testament Greek Lexicon as: "corporeal; bodily; having a bodily form or nature; pertaining to the body."
So at the time of Jesus’ baptism a materialized bird, a dove, did indeed descend from the sky and rest upon Jesus. That something material was observed is apparent from the words of John the Baptist as recorded at John 1:32-34. “I viewed the spirit coming down as a dove out of heaven, and it remained upon him. Even I did not know him, but the very One who sent me to baptize in water said to me, ‘Whoever it is upon whom you see the spirit coming down and remaining, this is the one that baptizes in holy spirit.’ And I have seen it, and I have borne witness that this one is the Son of God.”
The purpose of this materialized dove coming down was to convince John the Baptist that Jesus was indeed the Messiah, the Son of God, and that by means of his sense of sight. It therefore had to be just as real to his eyes as were the words, “This is my Son, the beloved, whom I have approved,” to his sense of hearing, to his ears. (Matt. 3:17)
This representation of the Holy Spirit as a dove calls to mind the manifestation of the Holy Spirit at Pentecost, as recorded at Acts 2:1-4. At that time it took the form of “tongues as if of fire” that became visible and rested upon each one of the 120 present in that upper room in Jerusalem. Of course, these were not burning flames, but “tongues as if of fire,” otherwise they would have burned the ones upon whom they rested. Yet they were something that was truly observable; just as were the flames that Moses saw at the thornbush at the time Jehovah God called and commissioned him to deliver his people from bondage. (Ex. 3:2)
What the Manifestations of the Holy Spirit Tell Us
The manifestations of the Holy Spirit are important in that they reveal the nature of the Holy Spirit. Notice that only once is the Holy Spirit manifested in the Bible as a living creature: a "dove" not a person. It is especially significant that the Holy Spirit is never shown in the form of a person since it is often described as a thing (e.g., being poured out or given out in portions; Numbers 11:17; Acts 2:17, 18, 33). (See: The Holy Spirit is an "it" that can be distributed into portions; Search For Bible Truths)
The way that the Bible uses the term "holy spirit" indicates that it is God's active force that He uses to accomplish a variety of His purposes. (Genesis 1:2; 2 Corinthians 4:7; Acts 2:1-4)
Many historians and Bible scholars (most of them trinitarians) freely admit this. For example: "On the whole, the New Testament, like the Old, speaks of the Spirit as a divine energy or power." - A Catholic Dictionary.
And An Encyclopedia of Religion agrees:
"In the New Testament there is no direct suggestion of the Trinity. The Spirit is conceived as an IMPERSONAL POWER by which God effects his will through Christ." - p. 344, Virgilius Ferm, 1945 ed.
For more, see:
Holy Spirit - Links to Information (Search For Bible Truths)
God’s Active Force; Holy Spirit (Insight-2 pp. 1017-1027, Spirit; Watchtower Online Library)
The Bible’s Viewpoint - Is the Holy Spirit a Person? (g 7/06 pp. 14-15; Watchtower Online Library)