The Greek verb diazōnnumi means to gird oneself thoroughly or to wrap/fasten a garment tightly around the waist — typically as preparation for service or action. It appears in John 13 where Jesus girded Himself with a towel before washing the disciples' feet, and in John 21 where Peter girded himself before jumping into the sea to reach Jesus.
The girding imagery in John's Gospel carries enormous theological weight. Jesus girding Himself with a servant's towel (John 13:4) is a enacted parable of the Incarnation itself — the Son of God stooping to the lowest service. This act redefines greatness in God's kingdom: the one who girds himself to serve is the greatest. Peter's impulsive girding in John 21:7 to swim to Jesus shows the transformation of the one who had denied Christ — now rushing toward Him rather than fleeing. The call to 'gird your loins' throughout Scripture (Exodus 12:11, 1 Peter 1:13) is always a call to readiness for service and obedience.