Baptism And The Trinity

Et ecce vox de coelis dicens: Hic est Filius meus, in quo mihi complacui Ac si diceretur: In te placitum meum constitui, hoc est qui mihi placet, salutem generis humani. Sanctae vero Trinitatis in baptismo declaratur mysterium, dum Filius Dei baptizatur in homine, Spiritus Dei descendit in columba, Pater Deus sonat in voce; ut ostenderetur in nomine Patris, et Filii, et Spiritus sancti, credentes esse baptizandos. Sanctus Beda, In Matthaei Evangelium Expositio, Lib I, Caput III Source: Migne PL 92.18c

And behold a voice from heaven saying: This is my Son in whom I am well pleased. 1 As if it were said, 'In you my joy is established, this is He who pleases me, the salvation of the human race.' The mystery of the Holy Trinity is also declared in the baptism, for while the Son is baptised as a man, the Spirit of God descends as a dove, and God the Father speaks with the voice, that it be shown believers are baptized in the name of the Father and of the Son and of the Holy Spirit. Saint Bede, Commentary on the Gospel of Matthew, Book 1, Chap 3 1 Mt 3.17