When Moses informed God that he could not possibly be the one to confront Pharaoh on the mission of demanding the release of the Israelites, his reasons ranged from "they will not listen to me" to "I am not eloquent...I have [lit] a heavy mouth & a heavy tongue [Exodus 3-4]. It is rather humerous to listen to Moses debate God rather eloquently and then see him advance an argument to God that he was NOT eloquent. In your Bible I would ask you to write the word "irrelevant" next to Exodus 4:10. God's response was that He made Moses mouth and would teach him what to say. The reality was that Moses took too much on himself to believe that his eloquence was the key to the release of Israel from their slavery. It borders on subtle insanity to think that our gifts are the key ingredient to the success of any task or ministry for God. Repeatedly God told Moses throughout his preparatory period that it would be God's hand and God's power and God's sovereignty that would force Pharaoh's hand (Exodus 3:7-8; 3:16-17; 3:19-21; 4:11; 6:1; 6:5-8; 7:1;7:4-5). Moses only had to obey God's commands to deliver the message.
God warned Moses that Pharaoh would not listen (Exodus 7:4). If you were informed that what you would do and say in your ministry to God would not be observed to be successful, the temptation to quit would be overwhelming. It seems Moses wrestled with that...especially when the burdens increased upon his people as a result of the first unsuccessful attempt to secure their release from Pharaoh [Exodus 5]. But back to that "irrelevant" thing. In your Bible I would ask you to write the word "irrelevant" next to Exodus 7:4a. The issue is not whether the outcome is successful. It makes no difference whether Pharaoh listens or not. The issue is...do what God says. That is where we all, as believers, must live! Our productivity and our success lies not in what happens after the fact, but what happens before the fact...obedience to His word... His command. Let that word "irrelevant" resonate in your minds for a while, espeically when you are tempted to trust your own gifts and abilities as those ingredients necessary to make the difference. Think it through!