Joshua 5:15
NKJV - 15 Then the Commander of the LORD's army said to Joshua, "Take your sandal off your foot, for the place where you stand is holy." And Joshua did so.
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Your feet are what take you around in this sinful world. You walk to and from committing what ever sins or infractions your heart desires, thereby carrying the filth of this sinful world around with us. John 13:8-11.