The first sixteen verses of Matthew 20 should have been included in chapter 19, for the Lord Jesus gave this parable as a response to the events of Matt. 19:16-30. The Lord Jesus told the rich young man to give all his wealth to the poor and to follow Him and he would have treasure in heaven. The young man refused, but Peter asked, " We have forsaken all and followed Thee; what shall we have therefore?" This parable is given as part of the answer to Peter’s question.
The parable seems to say that Peter’s question is not a proper one. God is righteous and will distribute rewards as He sees fit. Only God can rightly judge the value of a person’s work. We should not attempt to judge the value of anyone else’s work and cannot rightly judge even our own. We know there will be no complaining in heaven before the judgment seat of Christ, but is there any complaining (audible or inaudible) among us here on earth? Do we wonder why a certain Christian has this or that and we don’t, when obviously we are more devoted to Christ? Do we want more recognition? "The last shall be first and the first last" (Matt. 20:16).
It would be spiritually healthy to remind ourselves frequently that it is lawful for God to do what He wishes with what is His own (verse 15). God is not only righteous, He is sovereign (He is in charge) and we can and must leave to Him the distribution of rewards, earthly and heavenly. Since no one has anything, spiritual or material, except by His grace, complaining is entirely out of order. Quite possibly, as God sees things, we are the workers who have worked only one hour and are getting far better than we deserve. Let us remember Christ’s words to His disciples which sum up another parable:"So likewise ye, when ye shall have done all those things which are commanded you, say, We are unprofitable servants; we have done that which was our duty to do" (Luke 17:10).