In Isaiah 7:25, this signifies doing good from the love of good. (Apocalypse Explained 304[12])

In Isaiah 5:6, this signifies unable to be cultivated, or prepared to receive. (Apocalypse Explained 644[9])

Our feet are the lowest parts of our bodies, and they're very useful! In the Bible, feet represent the lowest and most utilitarian part of our spiritual selves -- the “natural” level. This everyday aspect of life is involved with routine tasks and demands and the thoughts associated with them. It's not terribly deep or introspective, but it is useful -- just like feet. This correspondence is true of the Lord and of church communities, too. The Lord's Divine Natural leads us through relatively simple obedience (think of the Ten Commandments). Churches, too, have a natural level on which they serve their communities in simple but tangible ways.