//Kissing of feet is an important Christian religious ritual. Feet washing, which precedes the kissing, is a sign of humility[21] and is looked upon as an "act of lowly service, of loving service, and of self-giving service."[22] This caring act "reflects the grace of God’s never-ending, unconditional love and, as such, its observance is surely a means of grace with exceedingly strong sacramental characteristics."[22] Jesus washed the feet of his disciples and then commanded them to "wash one another's feet" (John 13:12) with love and humbleness as a service through which one can express "the love of God and the saving, cleansing grace of our savior Jesus Christ to each other."[22] After cleansing, a kiss would be bestowed on the feet as an act of servitude. By performing the actions of the lowliest servant, Jesus demonstrated what kind of servant-based leadership was expected from his disciples.//
Source
https://en.wikipedia.org/wiki/Kissing_traditions#Kissing_in_Christianity