Read Matthew 20:1-16.This parable really begins with Peter's question in 19:27: "We have left everything to follow you! What then will there be for us?" After Jesus reveals the disciples' special position in heaven, he goes on to point out that others that will follow Him will receive their reward. However, "many who are first will be last, and many who are last will be first." The parable in chapter twenty then explains that God is not bound to any rules we may device as to who receives what reward. He is sovereign and therefore, entitled to dispense the rewards as He sees fit no matter who came first. God's reward system does not have to match man's ideas of reward. He thinks way beyond our first, second, and third place ribbons. And as the Almighty Creator, He has the right to do so.
"So the last will be first, and the first will be last." NIV
But it must be clear, the main and most important and valuable reward is to be with Jesus Christ. Anything after that is pure gravy. I have already received His presence in this life through the Holy Spirit and will have the joy of the presence of the entire trinity in heaven. I shall see Him face to face. What more reward would I ever want? That is the ultimate gift. And if God wants to bestow more grace on someone who has followed Him for a shorter period of time than me, so be it. I will not debase the glory of being in His presence with the sin of jealousy. My cup is already full to overflowing.