Albert Barnes on Luke 3:22

In a bodily shape. This was a real visible appearance, and was doubtless seen by the people. The dove is an emblem of purity and harmlessness, and the form of the dove was assumed on this occasion to signify, probably, that the spirit with which Jesus would be endowed would be one of purity and innocence. The Holy Spirit, when he assumes a visible form, assumes that which will be emblematic of the thing to be represented. Thus he assumed the form of tongues, to signify the miraculous powers of language with which the apostles would be endowed; the appearance of fire, to denote their power, &c., Acts 2:3.