A.T. Robertson Commentary Mark 1:7

"And he preached, saying, There cometh after me he that is mightier than I, the latchet of whose shoes I am not worthy to stoop down and unloose." — Mark 1:7 (ASV)

Mightier than I (ο ισχυροτερος μου). In each of the Synoptics. Gould calls it a skeptical depreciation of himself by John. But it was sincere on John's part and he gives a reason for it.

The Latchet (τον ιμαντα). The thong of the sandal which held it together. When the guest comes into the house, performed by a slave before one enters the bath. Mark alone gives this touch.