Moses said to the Lord, "Please show me your glory" (Ex. 33:18). In effect, he asked, "Who are you, God?" God responded with these words: "I will make all my goodness pass before you and will proclaim before you my name 'The LORD.' And I will be gracious to whom I will be gracious, and will show mercy on whom I will show mercy" (v. 19). He promised to reveal Himself.
But no man can see God and live. That is too much for any man—sinful man in particular. God told him to stand on the rock and said, "While my glory passes by I will put you in a cleft of the rock, and I will cover you with my hand until I have passed by. Then I will take away my hand, and you shall see my back, but my face shall not be seen" (vv. 22-23). Moses did well in asking God who He is rather than telling God who he wanted Him to be. Thus, God was going to reveal Himself in part to Moses. He was going to pass by, protect him with His own hand, and proclaim His own name. This meant far more than simply pronouncing the name Yahweh—"LORD" in our English translations—in Moses' hearing. He was going to proclaim His nature:
And the Lord passed before him and proclaimed, "The Lord, the Lord, a God merciful and gracious, slow to anger, and abounding in steadfast love and faithfulness, keeping steadfast love for thousands, forgiving iniquity and transgression and sin, but who will by no means clear the guilty, visiting the iniquity of the fathers on the children and the children's children, to the third and the fourth generation." (34:6-7)
"The LORD, the LORD"—here God revealed Himself to Moses by His personal name, Yahweh. He is the great I Am. He is the self-existent, changeless God through whom all things exist, and He is merciful, gracious, longsuffering, full of goodness and truth.
Forgiveness is so important that it is expressed using three similar terms: "forgiving iniquity and transgression and sin." He abounds in forgiveness and mercy. But our God, according to His self-revelation, is also just. Our text states that He will not simply clear the guilty. It would be contrary to His nature to simply overlook sin. Justice must be done because of who God is. Our God must be true to who He is. But how can He be both merciful and just at the same time? How can He act in a way consistent with these two traits? If He shows only mercy, justice is set aside. If only justice is served, there is no mercy.
The answer is the incarnation and the cross. The Father, because He is both merciful and just, sent the Son to represent all whom the Father had given Him (John 17:18-23; Eph. 5:25-32). Without ceasing to be God, the Son took to Himself a human nature, and having been conceived of the Holy Spirit and born of the Virgin Mary, He lived perfectly under the law of God, keeping the law that Adam broke. He willingly went to the cross, having taken His elect, as their federal head (representative), to be one with Him, including our sin. He then bore the wrath of the Father, paying the debt that we cannot pay.
Paul says in 2 Corinthians 5:21, "For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God." By making us one with Jesus, the Father could have His wrath fall upon the Son. Justice was done, and our guilt was removed. At the cross of Jesus, we find both the amazing mercy and the perfect justice of God on full display.
Let's go back to Moses. He knew that no man could see God and live, but God said that while His glory passed by, He would put Moses in a cleft of the rock and cover the prophet with His hand. David knew this imagery well, saying, "The LORD is my rock and my fortress and my deliverer, my God, my rock, in whom I take refuge, my shield, and the horn of my salvation, my stronghold" (Ps. 18:2). And Paul makes it clear that the Rock of our salvation is Jesus (1 Cor. 10:1-4). Our God does for those who trust Christ what He did for Moses. He hides us in the cleft of the Rock. He hides us in Jesus. In Him, our sins are forgiven. In Him, we are saved from the wrath of God. In Him, we know both justice and mercy.