“the holy spirit.” The Greek text has no article “the.” This holy spirit was the gift of God that He gave to some believers before Pentecost. [For more information on the holy spirit and uses of “holy spirit,” see Appendix 11, “What is the Holy Spirit,” and also see Appendix 6, “Usages of ‘Spirit’”].
“descended onto him in a bodily form.” This event was visible to those who were there, for example, John the baptist saw it (John 1:32)