‘Take now thy son, thine only son Isaac, whom thou lovest.’ Strictly he wasn't the only son.
God spoke to Abraham, he speaks to us of course, through his word. He believed God’s word whatever difficulties stood in the way. We too must believe his word, his promises to us, and we must obey him and trust him no matter what. The apostle Paul has a wonderful term. He uses it twice in the letter to the Romans, and the term is ‘the obedience of faith’. If you believe in the Lord and trust him you will obey his every command.
What is the purpose of the trial of faith? One of the big purposes is to humble us. Everybody fights against pride in some form, and trials provide major times of humbling and recognising our weakness and need. Then, of course, they draw us to prayer. The test always brings us to God, whether it's a serious illness, whether something else has fallen apart in our life experience. They draw us to the proving of the Lord. As we appeal to God for help, he hears an answers prayer and there is revealed to us some blessing or deliverance that we would never otherwise have known.
Some find this so difficult. They say, ‘What Abraham possibly believed is that Isaac would be resurrected in future glory.’ But no, he believed, he concluded that God must bring Isaac back to life there and then, in order that the very specific promises concerning the great nation that would come from Isaac could be fulfilled. So he believed God with all his heart.