John Wesley on Exodus 34:29

The skin of his face shone - This time of his being in the mount he heard only the same he had heard before. But he saw more of the glory of God, which having with open face beheld, he was in some measure changed into the same image. This was a great honour done to Moses, that the people might never again question his mission, or think or speak slightly of him. He carried his credentials in his very countenance, some think as long as he lived, he retained some remainders of this glory, which perhaps contributed to the vigour of his old age; that eye could not wax dim which had seen God, nor that face wrinkle which had shone with his glory.