Sandals in the Bible are connected with the feet. Feet are connected with the WALK. The father is interested in our walk. The son was obviously barefooted. His feet/walk were exposed to stones, glass, injury of all kinds whilst unshod. When we are not walking with God, our feet, our lives are exposed to the pains which are caused by sin and transgression. When our feet, our walk is protected by the sandals we can walk in a way that is pleasing to our father. Sandals represent protection for the feet, a renewed walk, walking on a right path. See Psalm 1.
Paul also spoke of the feet being shod with the preparation of the gospel of peace. See Ephesians 6. There we can relate to the need for the feet to be prepared to walk or run with the gospel message. Without feet that are properly shodden or covered, they too will be exposed to the harshness of the road. It won't be long that we shall not be able to walk with the gospel. We need help.
We need to have feet that are properly prepared for the journey, wether the Christian life or the gospel.
How beautiful are the feet of them the publish the gospel of peace.