and having strapped on your feet the preparation of the gospel of peace; -Ephesians 6:15, NASB
“Strapped on your feet” is in reference to footwear.
The Roman soldier’s sandal had hobnails—short nails that had a thick head to improve durability on the battlefield and to keep the soldier from slipping. The gospel of Jesus Christ will keep us from slipping into deep depression—the wearies of this life and from losing our faith.
The sandal, which represents the gospel of peace, also suggest that believers are to spread the message of hope that is found in Jesus Christ—bringing peace to those who accept Jesus as their Lord and Savior. If we spread the gospel to the unsaved and conform our life according to the gospel of Christ—the enemy won’t be able to make us fall away from the Lord. The gospel keeps our feet firmly grounded in the truth—keeping us from being deceived.