Joseph Stump - An Explanation of Luther's Small Catechism

The Ten Commandments are not numbered in the Bible. A two-fold numbering is found among Christians. The first is that which is given in our Catechism, and which is accepted by the majority of Christians, The other numbering makes two commandments of our first (the second being the command not to make any images), and joins our ninth and tenth into one. This makes a difference in the numbering of all the commandments except the first.

When God gave the commandments to Israel, He forbade them to make any graven images or likenesses. God being a Spirit, the making of an image of God would at that period necessarily have resulted in idolatry. But since Christ has come in the flesh and was visible among men, we are permitted to make pictures and images of Him. Luther preached very forcibly against those persons who, during his absence from Wittenberg, destroyed the pictures and images in the churches. He said that we make a picture of Christ in our heart whenever we think of Him, and put pictures of Him in the Bible and other books; and that therefore it is not wrong to place pictures or images of Him in our churches, so long as we do not worship them.