Jesus' first entry into Jerusalem was a humble way to signify that he was the King of peace, and that he had chosen to enter the city on a donkey. In the Bible, John 12:15 says, "Do not be afraid, Oh Daughter of Zion; see, your King is coming, seated on a donkey's colt". Riding a donkey is a way to signify peace, while a horse would have been a symbol of war. In the Bible, donkeys are also portrayed as symbols of service, suffering, peace, and humility.
In his second coming, Jesus will come to earth as a conquering ruler, dispossessing Satan's rule. He will judge and wage war in righteousness, and rule the nations of the earth with a rod of iron.