Why did Moses have to take off his sandals?

In your teaching in Ruth teaching, taking off the sandal was done by the one who failed to redeem. If Moses had to take off his shoe was it because Moses had fled Egypt and failed to redeem Israel at the time he fled?

Your observation was excellent, but it leads to a slightly different conclusion than the one you offered. First, we should be clear on the literal meaning of the text in Exodus 3. Moses was instructed to remove his sandals, because he was standing on holy ground. The meaning is clear: God demanded that Moses humble himself in the presence of a holy God.

But as you suggested, there is a deeper meaning as well. If you remember, Moses is offered in Scripture as a type (or picture) of the Law. Since we know the Law can never be the means by which men may reach heaven (i.e., we can't enter heaven by works of the Law), Moses is used frequently as a picture of this truth.

For example, we know that Moses wasn't permitted to lead the Israelites into the Promised Land. Instead, Moses died in the desert, and Joshua (which is Yeshua in Hebrew or Jesus in Greek) was the one to lead the Israelites into Canaan. Through this example, we see how Moses was used as a type of the Law, in the way the Law cannot lead men to heaven, only Yeshua (Jesus) can.

Likewise, in your example we can also see Moses being used as a type of the Law. The Law was never intend to be the means for redeeming men form sin, as Paul says clearly in Romans 3:20-21:

Because by the works of the Law no flesh will be justified in His sight; for through the Law comes the knowledge of sin.
But now apart from the Law the righteousness of God has been manifested, being witnessed by the Law and the Prophets,

So as a redeemer, Moses was unable to serve God's purposes. In that sense, he "removed his sandals" and it was left to God to be the redeemer of Israel and all men.