Moses is not allowed to see God face-to-face, but does receive a disclosure of the character of God.
"I will be gracious to whom I will be gracious, and will show mercy on whom I will show mercy." These words should be read in the context of Israel's disobedience at Sinai. It is also important to recognize that the text does not develop a correlate: "I will punish whom I will punish, and will destroy whom I will destroy." The words of 33:19 are not an expression of arbitrary sovereignty. The penalty for idolatry was death (22:20). God would have been justified in abandoning Israel to total destruction. "I will be gracious to whom I will be gracious…" is an assertion that God can transcend punitive retribution. In later prophetic preaching the announcements of judgment contained rationales; Israel's conduct is cited as a reason for the judgments and destruction that are announced. In contrast, the announcements of hope are not grounded in a rationale growing out of human conduct. Deliverance, restoration, and transformation are based in God's decision to forge a future where there is only condemnation and death. "I will be gracious to whom I will be gracious…" opens doors to a future where human beings can neither imagine one nor confidently guarantee one.
Paul, in Romans 9, draws upon this verse to argue that God in Christ could open the covenant to include Gentiles. God could break beyond God's own covenant with Jacob. This is not an argument for the Gentiles displacing Jacob; rather, in Christ God is not limited to Jacob. Exodus 33:19, in context, is not going that far, but in asserting God's sovereign freedom to be gracious, a wide door is already opened. Given the severity of the covenant breach in making the golden calf, we should linger in astonishment over God's graciousness in continuing a relationship with Israel before rushing to the New Testament inclusion of Gentiles.
19And he said, I will make all my goodness pass before you, and will proclaim before you the name, The Lord;* and I will be gracious to whom I will be gracious, and will show mercy on whom I will show mercy.
New Revised Standard Version Bible: Anglicized Edition, copyright © 1989, 1995 National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved worldwide. http://nrsvbibles.org