What does he mean by “Your glory”? Is it that he is sure God exists but needs to know that He really is glorious?
“Your glory” indicates something much deeper. “Show me Your essence” is what Moses is asking.
How does God respond? “You cannot see Me, but I will let you see My effect on nature”.
It has been said that this is like someone who sees steps in the snow. By following the steps and discovering their characteristics, you can see something of the walker who has been there, but the walker him- or herself you will never see.
So when the challenge comes – “Show me that there is a God” – our answer has to be, “Look and I will show You where God has been, what He has done, the way He has changed the world because of His presence”.
When someone says, “What has God ever done for me?”, you can possibly follow Rashi by indicating the spiritual rewards that God has bestowed on the individuals who found grace in His sight, but it may be better to point to the gifts God has given to humanity as a whole.
Some are gifts which show themselves in every generation: some are manifest at particular times.
When the Torah says at the beginning of Genesis (Gen. 3:8) that Adam and Eve perceived the voice of the Lord “walking in the garden l’ru’ach hayom, in the cool of the day”, it is possible to understand l’ru’ach hayom as “in the spirit of the day”, i.e. according to the nature of the moment.