What does Matthew 20:16 mean?

This verse bookends this passage with Matthew 19:30. Jesus had assured the disciples of a rich reward in the kingdom of heaven for all they have given up for His sake, as well as eternal life. He had added, though, that many who are first will be last, and the last first, in the kingdom of heaven (Matthew 19:27–30). Then He told the parable in this passage (Matthew 20:1) to illustrate what He meant by that.

Now Jesus makes the same statement in reverse order to show that He has explained what it means that the last will be first, and the first last. That may be, but not all commentators agree about what exactly He meant.

Some suggest the parable is about Israel and the Gentiles who will come into the kingdom by faith in Christ, making those who come through Christ first even though they came to be included in the family of God last. Others hear Jesus describing a general reversal in the kingdom of position and status on earth, making the rich poor and the lowly great. Still other teachers believe the meaning of the parable should be restricted to the disciples themselves to quiet their arguing about who was greatest among them.

The bottom line of the parable, however, seems to be that all are received and rewarded by God based on His grace. He gives much to those He wishes to, in Christ, based not on their worthiness but on His own generosity. Some of those who are last, least deserving of reward in the kingdom of heaven, may become first in receiving God's grace precisely because of their lack of apparent work or effort. Others who gave up much for Jesus and seemingly did great things for God may be last in terms of their apparent relative reward. It is all for God to say.