Amos started prophesying about 40 years after Elisha. If Gehazi (Elisha's servant) had not chased after Naaman's money and thus ruined himself, it is possible that he may have got a double portion of Elisha's anointing and become the next prophet in Israel. In that case, Gehazi may have written this prophecy instead of Amos. But Gehazi missed that privilege. The Lord warns us to be watchful so that no one takes our crown (Rev.3:11). There is a crown that God has kept for you if you will be faithful in the ministry God planned for you. But you can lose that crown if you are unfaithful. And then the ministry you were supposed to fulfil will be done by somebody else and he will get your crown. So perhaps Amos got Gehazi's crown!
Amos had no desire to be a prophet. He was a simple shepherd - just like many of the first apostles were simple fishermen. Elisha had been a farmer. Amos was a man who looked after cattle, sheep and figs. When questioned about his credentials he said, "I am not a professional prophet. I certainly never got any training to be a prophet. I am just a shepherd. I take care of fig trees. But the Lord called me away from my flock and told me, �Go and prophesy to My people in Israel' " (Amos.7:14-15).
Why did God pick Amos to be the first person to write down a prophetic message? God must have watched him (like He watches all of us) to see if Amos feared God and was faithful in his work. Amos was not a scholar or a priest, but he was very faithful in his work. He was God-fearing, was kind to poor people and lived in a good way. And one day, God called him and told him, "You are going to be My servant."
God watches us every day to see if we are faithful in our daily life, whether we choose the way of humility always, whether we take time to wait on Him and listen to Him, to study the Scriptures, etc. Maybe Amos had been faithful for 25 years, I don't know. I know that Jesus was faithful for 30 years in Nazareth before He was called to preach. When you continue being faithful in little things for many long years, you can begin to wonder whether God has forgotten all about you. He has not. All of a sudden, one day, God will say to you, "You are My servant from today." God calls those who are faithful in their secular work. He did that in the Old Testament. Jesus also called as apostles men who had been faithful in their secular work.