So he doubted God and had a child with Hagar.
I believe that God wanted to have Abram to listened to him. God wanted to send a message to Abram because of the future pact.
God asked Abram to obey. Obedience is important in a believer's life. The believer needs to ask the Lord to guide the human desire.
God promised a pact with Abram. God will use Abram to have a country. The country is called Israel. He wanted the Jews to wrote the Words of God. God promise that he would increase the population of the Jews.
Abram was amazed by the power of God. It is amazing when God speaks to mankind.