When Moses encountered God in the burning bush on the mountain at Horeb, God called Moses to be the instrument of leading the Hebrew people out of Egypt.
Moses immediately questioned God as to the his own qualifications for the task.
Who am I that I should go to Pharaoh and bring the children of Israel out of Egypt?
God responded that He would be with Moses and promised a sign to him.
At this point the reader of the text would probably expect for God to do something miraculous at that moment to convince Moses. However, the sign that God would give to Moses – a sign confirming that Moses’ qualification was that God would be with him – was not an immediate sign.
This shall be the sign for you, that I have sent you, when you have brought the people out of Egypt, you shall serve God on this mountain.
Do you see the timetable? God’s sign would not happen until after Moses completed the task. In the meantime, Moses would have to take God at his word. He would have to demonstrate faith.
Do not miss the connection between those two components. God’s word led to Moses’ faith. It was not a blind faith. It was not an unfounded faith. It was a belief that God would do as he said. After all was said and done, then God would confirm via a sign that He had indeed called Moses to the task.