Now John was lclothed with camel’s hair and wore a leather belt around his waist and ate mlocusts and nwild honey. 7 And he preached, saying, o “After me comes he who is mightier than I, the strap of whose sandals I am not worthy to stoop down and untie. 8 pI have baptized you with water, but qhe will baptize you with the Holy Spirit.” 
John is dressed as a prophet and, according to Josephus was a man of significance.
for Herod slew him[John the Baptist], who was a good man, and commanded the Jews to exercise virtue,
both as to righteousness towards one another, and piety towards God, and so to come to baptism; 
John had a significant following (v5) but looked to one who would come who would be ἰσχυρότερός than him. This word has a faitly loose meaning but could be translated as stronger, mightier or more powerful. John clarifies what he means by saying.
a) not worthy to undo sandals
b) the coming one will baptise with the ‘Spirit’
John was looking for someone is stronger. The LXX often uses the word ἰσχυρότερός to speak of YHWH, ans some one who will bring the spirit. Reading this verse alongside verses 1+2 we can suggest that John is looking for the ghreat coming day of salvation which is proclaimed by Isiaiah 40-55 , the return of YHWH to his people, his presense with them forever. John is urging his followers to prepare themselves mentally and spiritually for this day. The following quote makes the point better than I ever could.
It is Yahweh who will follow the forerunner in both Mal. 3:1 and Is. 40:3, and in OT thought it is Yahweh himself who will pour out his Spirit in the last days (Is. 32:15; 44:3; Ezk. 36:26–27; 39:29; Joel 3:1–2 [EVV 2:28–29], etc.). It says a lot for the underlying christology of Mark’s gospel that he can allow the Baptist’s words, which in themselves point directly to the coming of God, to be read as referring to the human Jesus. For him, apparently, the coming of Jesus is the eschatological coming of God. 
It’s Christmas tomorrow and remember the son of God who came to pitch his tent with us (John 1). Likewise we see in ther begiing of Mark that Jesus is no other than the presence of YHWH with his people. Emmanuel-God is with us!