The conjunction δὲ serves to move the reader off of the main event of the baptism onto a dialog between Jesus and John.1 The article ὁ begins the sentence and in the case of Ἰωάννης not being part of the text as discussed in "Textual Variants" above (p6) would function as a pronoun . The force of δὲ as an adversative conjunction would then become a "switch-reference device"2 indicating that the speaker indicated by the article is no longer Jesus requesting baptism but rather has become John trying to prevent Jesus. Either way it is clear that John is now the speaker whose actions and speech exhibit a misunderstanding of what exactly Jesus is coming for. The baptizer rightly perceived a moral mismatch between himself and Jesus and thus when Jesus came to him, he tried unsuccessfully to stop him from being baptized.
Matthew is the only synoptic writer to comment on this discussion. Some commentators seem to think Matthew inserted the discussion to protect against the opinion that Jesus had sins to repent of. The verb διεκώλυεν is a tendential imperfect3 indicating that John's attempt at prevention was at least vocal. Most modern versions adequately capture the incomplete and unsuccessful nature of John's attempt by saying in some way that John "tried" to stop Jesus. The KJV however simply translates it almost as an historic aorist using the archaic "forbad".
The adverbial complimentary participle λέγων describes how it was that John tried to prevent Jesus' baptism. There is no indication either in favor of or against John pushing Jesus away or otherwise physically attempting to stop his cousin. Nevertheless it was a passionate speech which John must have begun with Jesus. The personal pronoun ἐγὼ intensifies the contrast4 between John (ἐγὼ) and Jesus (σοῦ); and effectively demonstrates John's apparent dismay that Jesus would come to him.
While it seems evident that his argument is based on Jesus not needing baptism, the first reason given is John's personal acknowledgment of sin. "I have need…," John says, placing the noun χρείαν5 in the forward position for emphasis. Keener argues that John was seeking a baptism which is different in kind than that which John had been offering "…John recognized that Jesus had come to bestow the Spirit in fuller measure than even he as a prophet had received, and he desired this baptism…"6 But John 1:33 indicates that John the Baptist was not fully aware of Jesus' identity until after the baptism. Therefore it could not have been his knowledge of Jesus being the Christ which
Grammatically the passage is introduced by the temporal adverb Τότε which serves to connect these events to the introduction of the then unknown Messiah which John delivers in Matthew 3:11-12. It also demonstrates that the current passage occurs not long after John's announcement. Of the eighty-nine times Matthew uses τότε, more than half of the time its use is to draw a close chronological connection or to point out a response to the prior section. As has already been noted1 Dr. Hoehner dates the coming of John the Baptist to the year 29AD and the resultant baptism of Jesus during the summer or fall of the same year.2
The appearance of Jesus is significant in this passage because it is his first autonomous activity. As far as Matthew's gospel is concerned we have only seen him as a secondary participant up to this point. His birth, move to Egypt and subsequent move to Nazareth have all been actions centered in his mother and Joseph. Now for the first time, Jesus becomes the central actor. By tying the introduction of Jesus then to the activity of John the Baptist, Matthew effectively demonstrates for his Jewish readers that Jesus is fulfilling the Messianic prophecies of scripture (Matthew 3:3, Isaiah 40:3).
The reader is drawn into the scene by the same historical present verb (παραγίνεται) which is used in the first verse of the chapter concerning John. So that as John came dramatically onto the scene with a distinctive purpose, so also does Jesus.