At Mount Sinai God's people received the revelation concerning God Himself that they might be separated unto the holy God as His sanctified people (Exo. 20—24). By the revelation of God Himself, we refer to the law. The law is a portrait of God. Before the children of Israel received the revelation concerning God's building, God gave them a portrait of Himself to show them what kind of God He is. The law reveals that God is a God of love and light and that He is holy and righteous. Therefore, love, light, holy, and righteous are crucial words describing the characteristics of the almighty, Triune God. As the God of love and light, He is altogether holy; that is, He is uncommon, different, and separate from everything else in the universe. Furthermore, God is altogether righteous. He is righteous with Himself, He is righteous in all He does, and He is righteous toward man and all His creatures. This is God as He is revealed in the picture in Exodus 20—24.
In the New Testament we have a description of God, but we do not have a picture of God. John tells us clearly that God is love and light, and Paul tells us that the very God who is love and light is absolutely holy and righteous.
The Ten Commandments are a type signifying Christ as the portrait of God, as the expression of God's image. Hebrews 1:3 says that the Son of God, Jesus Christ, is the express image of God's substance. Using a modern term, we may say that Christ is a photograph of God. To see Him is to see God.
The law is also a portrait of God. By studying the commandments of the law, we can see that God is love and light and that He is holy and righteous. Because the law is such a picture of God, the law was called the testimony of God (Exo. 25:16, 21; 31:18). The ark in which the law was placed was called the ark of the testimony (Exo. 25:22), and the tabernacle was called the tabernacle of testimony (Exo. 38:21). In the Psalms the law is often referred to as the testimony (Psa. 19:7; 25:10; 119:2). This testimony was a portrait, a picture, of God.
God's people received the revelation concerning God Himself so that they might be separated unto the holy God as His sanctified people. This matter is given particular emphasis in the book of Leviticus. For example, Leviticus 11:44 says, "I am Jehovah your God; you shall therefore sanctify yourselves and be holy, for I am holy."