Why does God repeat the same message over and over? Joel

Sometimes God has to give a message to us more than once.   In the book of Joel we read the same message as his contemporary, Zephaniah. Both of these prophets are telling us about the coming day of the Lord.   They are both warning the nation of the same thing.   God has to tell us more than once because we are dull of hearing spiritual things.   In the gospel we see Jesus telling the Pharisees and Disciples the same things over and over.  In Paul's writings we see the same themes and, sometimes, the exact words to different audiences (Romans and Galatians) and some times to the same audience (1 and 2 Corinthians).  The Bible message is not a complex system of religious rhetoric.   It is a message of God's Love, unfolded by His Mercy and Grace and supported by His perfect justice all directed depraved man.   Yet, we make it difficult and we reject it and we ignore it.   So, God has to repeat it.  Here He has to repeat the warning that they are going into captivity because of the sin and God is going to judge them and unbelievers for disbelief and disobedience.   They won't listen.   God will send more prophets.   Jesus was the last one.   They didn't listen to Him either.