David described the angels present when God spoke his law at Mount Sinai as "the chariots of God" (Psalm 68:17). His fine symbolism reminds us of the awesome majesty of God at the giving of the law. However, the angels were merely the symbols of the majestic glory of God while His law itself was the essential revelation of it. Thus, the Ten Commandments, even more than the angels at Sinai, may be called God's chariots of fire.
The voice of God at Sinai must forever be a voice of condemnation unless God had something more to say. He had, and He said it at Calvary. Out of the darkness of the cross the Lord Jesus Christ cried with a loud voice, "It is finished!" (John 19:30). Here is the voice of salvation from Him who perfectly fulfilled the law. Though no angels were present at Calvary when the Lord Jesus Christ died as a sacrifice to put away God's wrath and our sin, the chariots of God were there. His majesty was never more clearly revealed and His law was never more strictly in force than at the cross.
We may say that God rode down from glory to Mount Sinai in the chariots of fire to state His law, closing heaven against us as lawbreakers, but Christ our Saviour rode up to glory from Mount Calvary in those same chariots of God, opening heaven for us by His perfect satisfaction of the law.