The Holy Theophany

Matthew 3
   13 Then Jesus came from Galilee to John at the Jordan to be baptized by him.  14 And John tried to prevent Him, saying, "I have need to be baptized by You, and are You coming to me?" 15 But Jesus answered and said to him, "Permit it to be so now, for thus it is fitting for us to fulfill all righteousness."  Then he allowed Him.  16 Then Jesus, when He had been baptized, came up immediately from the water; and behold, the heavens were opened to Him.  17 And suddenly a voice came from heaven, saying, "This is my beloved Son, in whom I am well pleased."

Commentary by St. John Chrysostom:  
 

  Why do you marvel if He vouchsafed also to be baptized.  For the amazement lay in that one thing, that being God, He would be made man; but the rest after this all follows ...For righteousness is the fulfilling of the commandments.  "Since then we have fulfilled the rest of the commandments," He says, 'and this alone remains, it also must be added: because I have come to do away the curse that is appointed for the transgression of the law.  I must therefore first fulfil it all, and having delivered you from its condemnation, in this way bring it to an end ... Why were the heavens opened?  To inform you that at your baptism this is done also, God calling you to your country on high ...But why in the fashion of a dove?  That creature is gentle and pure.  Forasmuch then as the Spirit also is a 'Spirit of meekness' (Gal. 6:4), He therefore appears in this way.  And besides, He is reminding us of an ancient history.  For so, when once a common shipwreck had overtaken the whole world, and our race was in danger of perishing, this creature appeared, and indicated the deliverance from the tempest, and bearing an olive branch (Gen.8) ...all of which was a type of things to come ...Henceforth He leads us away from the old to the new polity, both opening us the gates on high, and sending down His Spirit from thence to call us to our country there ...for He has caused us (by baptism) to become 'sons of God,' and 'beloved' in fulfilling all righteousness.' and so He draws us towards that portion of ours.
  St. John Chrysostom.  Homily XII on Matthew III, 1, 3, 4.  B#54, pp.75, 76, 77, 78.