Why did the Jews from Moses onward need signs?
From Moses onward, the Jews needed signs in order to be convinced of what God was saying and what He was doing. This pattern continued throughout their history, as they required visible confirmation of God's message and actions. That is why signs were necessary for them.
Les explains that the Jews, beginning right with Moses and all the way up through their history, had to have signs in order to be convinced of what God was saying and what He was doing. Before looking at the sign aspect, Les directs attention to 1 Corinthians chapter 1, where Paul lays out the wisdom that comes only from God and not from men. Paul writes that not many wise men after the flesh, not many mighty, not many noble, are called. But God has chosen the foolish things of the world to confound the wise, and the weak things of the world to confound the things which are mighty. Les puts this in perspective with Moses: when Moses was mighty, had power, and had clout, God could not use him. Moses went out in the energy of the flesh and thought he could deliver the children of Israel. So God had to put Moses on the backside of the desert for 40 years to prepare him as an instrument God could use.