What does Mark 1:7 mean?

John the Baptist completely understands his role as prophet. He is not the Messiah, the savior promised to rescue the Jewish people, rather he is the one God has commissioned to prepare the way for the Messiah. John's camel-hair clothing and diet of honey and locusts reflect his humble approach to the task God has given him.

John's humility continues in claiming he is not worthy to stoop down and untie Jesus' sandals. When a visitor arrived at a Jewish home, the host would prepare a basin of water for the traveler to wash his feet. If the visitor was particularly important, he would remove his own sandals and a servant would wash his feet. It was assumed that the visitor was already ceremonially clean, and only needed to rinse the dust off. But not even a slave was forced to remove another persons' sandals. And yet, John the Baptist claims he is not worthy enough to even untie Jesus' sandals. He might mean he is not worthy to even prepare to wash Jesus' feet. Imagine John's shock when Jesus asks John to baptize him (Matthew 3:13–15)!

That Jesus washes His disciples' feet at the Last Supper shows what value He places on humility and servanthood (John 13:1-11).

John offers several contrasts between his role and that of the Messiah. He is a servant, while the Messiah is the master. He lacks power, while the Messiah has much power. His message and baptism of repentance is only a small taste of the baptism of the Holy Spirit Jesus would offer. John lifts the Messiah up as the one to worship and lowers himself as a humble servant of the Lord. Jesus, in return, lifts John up as the greatest born of women (Matthew 11:11).