Exodus 4:13

It became a serpent. Since Moses’ faith was not yet strong enough to rely on the future sign promised him (Exodus 3:12), God provided immediate signs by which he might validate his mission. These three signs were intended to convince the Israelites of the fact that God had appeared to Moses, but served at the same time to strengthen Moses’ faith and dissipate his fear of failure. This was to be evidence that God had called Moses to be the leader of Israel and endowed him with the power to discharge this responsibility.

Send, I pray thee. When all the excuses Moses could offer were proved invalid, his hidden motives in making them became obvious. What had at first appeared to be doubt of his own ability was now revealed as distrust of God (see v. 19). For practical purposes he refused to go. His curt, almost rude, answer to the divine commission is even more emphatic in Hebrew than in English.