Charles H. Spurgeon on Psalms 5:12

"With favour wilt thou compass him as with a shield." The shield is not for the defence of any particular part of the body, as almost all the other pieces are: helmet, fitted for the head; plate, designed for the breast; and so others, they have their several parts, which they are fastened to; but the shield is a piece that is intended for the defence of the whole body. It was used therefore to be made very large; for its broadness, called a gate or door, because so long and large, as in a manner to cover the whole body. And if the shield were not large enough at once to cover every part, yet being a movable piece of armour, the skilful soldier might turn it this way or that way, to catch the blow or arrow from lighting on any part they were directed to. And this indeed doth excellently well set forth the universal use that faith is of to the Christian. It defends the whole man: every part of the Christian by it is preserved. . . . . The shield doth not only defend the whole body, but it is a defence to the soldier's armour also; it keeps the arrow from the helmet as well as head, from the breast and breastplate also. Thus faith, it is armour upon armour, a grace that preserves all the other graces. William Gurnall.