I) [Mt 19:27-30]:
(v. 27) '''Peter answered him, "We have left everything to follow you! What then will there be for us?"
(v. 28) Jesus said to them, "I tell you the truth, at the renewal of all things, when the Son of Man sits on his glorious throne, you who have followed me will also sit on twelve thrones, judging the twelve tribes of Israel.
(v. 29) And everyone who has left houses or brothers or sisters or father or mother or children or fields for My sake will receive a hundred times as much and will inherit eternal life.
(v. 30) But many who are first will be last, and many who are last will be first."
Notice that this passage leads into and is introductory to the parable beginning in verse 20:1, which is about the same wage for different amounts of work in the field - a passage about rewards for believers, not how to work for eternal life. This is easily discerned from the beginning of 20:1 which starts with "For" connecting vv. 29-30 to 20:1 as a connected context and the end of the parable which parallels v. 19:30: "But many who are first will be last, and many who are last will be first". Neither section in Matthew could be about getting into heaven for both end with "first will be last... last will be first" and not how some will go to heaven and some to hell based on their relative service to God. Hence what we have in view throughout is working for relative rewards in heaven where the first on earth will indeed be last in rewards in heaven and vice versa, reflecting on Whom does one serve, onself to be first or God so that one's self is last.
[The Bible Knowledge Commentary, NT, Walvoord & Zuck, Victor Books, USA, 1988, p. 65]:
"In the previous incident Jesus told the rich young man to sell all he had and follow Him. This was exactly what the disciples had done, as expressed by Peter. We have left everything to follow You! What then will there be for us? Whereas the young ruler did not leave his possessions, (v. 22), Peter and the other disciples had (4:18-22; 9:9; cf. 16:25). Surely then, Peter reasoned, God would bless them for they were not trusting in their wealth! The Lord explained there would be a renewal (palingenesia, "rebirth") of all things. Though the nation was then rejecting His offer of the kingdom, the kingdom would come, with its extensive remaking of things spiritual (Isa 2:3; 4:2-4; 11:9b), political (Isa 2:4; 11:1-5, 10-11; 32:16-18), and geographical and physical (Isa 2:2; 4:5-6; 11:6-9; 35:1-2). Christ will then sin on His glorious throne (cf. Matt. 25:31; Rev. 22:1).
The disciples will have a special place in the kingdom, sitting on thrones and judging the 12 tribes of Israel (cf. Rev 21:12-14). In fact all who leave their homes and relatives for the Lord's sake will receive physical blessing that will more than compensate for their losses (Matt 19:29). This will be in addition to their eternal life in His kingdom. While it might appear they are giving up everything now and are the last, they will be given everything eternally and will be first. Conversely those, like the rich young ruler, who appear to have everything now (the first) will discover one day they have lost everything (they will be last; cf. 20:16).
II) [Mt 20:1-16]:
PARABLE OF THE VINYARD WORKERS
"(v. 1) "For the kingdom of heaven is like a landowner who went out early in the morning to hire men to work in his vineyard.
(v. 2) He agreed to pay them a denarius for the day and sent them into his vineyard.
(v. 3) About the third hour he went out and saw others standing in the marketplace doing nothing.
(v. 4) He told them, 'You also go and work in my vineyard, and I will pay you whatever is right.'
(v. 5) So they went. "He went out again about the sixth hour and the ninth hour and did the same thing.
(v. 6) About the eleventh hour he went out and found still others standing around. He asked them, 'Why have you been standing here all day long doing nothing?'
(v. 7) " 'Because no one has hired us,' they answered. "He said to them, 'You also go and work in my vineyard.'
(v. 8) "When evening came, the owner of the vineyard said to his foreman, 'Call the workers and pay them their wages, beginning with the last ones hired and going on to the first.'
(v. 9) "The workers who were hired about the eleventh hour came and each received a denarius.
(v. 10) So when those came who were hired first, they expected to receive more. But each one of them also received a denarius.
(v. 11) When they received it, they began to grumble against the landowner.
(v. 12) 'These men who were hired last worked only one hour,' they said, 'and you have made them equal to us who have borne the burden of the work and the heat of the day.'
(v. 13) "But he answered one of them, 'Friend, I am not being unfair to you. Didn't you agree to work for a denarius?
(v.14) Take your pay and go. I want to give the man who was hired last the same as I gave you.
(v. 15) Don't I have the right to do what I want with my own money? Or are you envious because I am generous?'
(v. 16) "So the last will be first, and the first will be last." '''
[BKC, p. 66]:
[Re: v. 16]: "By this illustration, Jesus was teaching that the matter of rewards is under the sovereign control of God, the 'Landowner' in the parable. God is the One before whom all accounts will be settled. Many who have prominent places will someday find themselves demoted. And many who often find themselves at the end of the line will find themselves promoted to the head of the line: The last will be first, and the first will be last.... In the final accounting, the Lord's analysis will carry the greatest and only important weight."