The Lord Jesus told this parable to illustrate the statement He made that "many who are first will be last, and the last will be the first" (Matthew 19:30).
The statement was made shortly after He had informed the award which would be given to those who had left family and property to follow Him. Therefore, it is logical to assume that it is part of the same subject, and does not concern the entry into the Kingdom of God that preceded it.
The parable is very simple, but the following points are worth enhancing:
Those who had been hired first, now expected to be paid more than the others who had worked less, and when they were paid the same (one denarius), they grumbled among themselves against the landowner, saying that this was unfair because they had worked much longer.
The owner contested this, telling one of the complainants that he had done no wrong, for he had paid him the denarius agreed upon when he was hired. It was lawful for him to do what he liked with his own things. The Lord Jesus reiterated here that (at the time of regeneration, chapter 19:28) "the last will be first and the first shall be last".
At first glance, it might seem that the parable refers to salvation and eternal life, granted equally to all those who believe, no matter their age, the seriousness of their forgiven sin, or the good or evil that they did. This is true, but it may not be what He was referring to. In the parable, we see that the payment was made for services provided, while salvation comes by God's grace, and not by merit, work or effort of those saved.
When they agreed to work for the landowner, the workers submitted to his lordship, and worked in this condition. This compares well to those who are saved by grace, and thus submit to the lordship of Christ.
In the parable, we find differences between the conditions of employment, length of service and the order of payment to the various workers. We also see a difference in the degree of generosity of the owner. All equally received enough to sustain them for one day.
The conditions of employment were different:
The first made a contract for a specified time, at a fixed price. At the end of the day they received exactly what was agreed, with which they should be satisfied.
Those invited to work later in the day received only a promise of a fair payment, but went to work relying on the fairness of the landowner.
Like the landowner, the Lord Jesus calls upon his redeemed people to be useful in His work in the world.
Some want to know the conditions of His work and even ask for rewards for themselves. So did some of His disciples (Matthew 19:27, 20:21 -24). They are not willing to work without first knowing what they are going to get in return and make sure it is enough for their needs.
Others will work for the Lord trusting entirely on His promise that they will receive what is right. Their faith in the Lord and the love they have for Him can lead them to great sacrifices in material and family terms (v. 29), but they leave entirely to the discretion of the Lord the decision about their reward.
All will be rewarded amply, those who work by faith being given the same as those who set their remuneration.
As for length of service, every believer is invited to take part in the Lord's work, one way or another. He may be young and live for many years, or have few years to work in between his conversion and his death. The Lord Jesus, in His grace, will reward in the same way he who had few years available as he who had many.
There was, however, a discrimination between the workers of the parable: the order they were placed in for payment. We understand that the first were the most honoured, yet served for the least time, having been the last to be called. They served by love and by faith, without selfish motives. Those who want big rewards and high positions for themselves in this world will be relegated to the lowest positions in the Kingdom of Heaven, no matter how much or how long they worked.
This chapter ends with the sentence "for many are called, but few chosen", which is repeated in Chapter 22:14.
It may be understood in two ways:
The Gospel is proclaimed to the whole world, but only those who convert and submit themselves to the lordship of Jesus Christ are chosen to participate in the Kingdom of Heaven. It is the sense in which it appears in Chapter 22.
Of all who will be entering the Kingdom of Heaven, relatively few are chosen for dedication to the work of God, as were the apostles and those we know as missionaries and workers. This interpretation is not very welcome in some circles for implying in a distinction that could lead to clericalism, with practices and teachings that the Lord hates (Nicolaitans, Revelation 2:6, 12:15).
1 "For the kingdom of heaven is like a landowner who went out early in the morning to hire laborers for his vineyard.
2 Now when he had agreed with the laborers for a denarius a day, he sent them into his vineyard.
3 And he went out about the third hour and saw others standing idle in the marketplace,
4 and said to them, 'You also go into the vineyard, and whatever is right I will give you.' So they went.
5 Again he went out about the sixth and the ninth hour, and did likewise.
6 And about the eleventh hour he went out and found others standing idle, and said to them, 'Why have you been standing here idle all day?'
7 They said to him, 'Because no one hired us.' He said to them, 'You also go into the vineyard, and whatever is right you will receive.'
8 "So when evening had come, the owner of the vineyard said to his steward, 'Call the laborers and give them their wages, beginning with the last to the first.'
9 And when those came who were hired about the eleventh hour, they each received a denarius.
10 But when the first came, they supposed that they would receive more; and they likewise received each a denarius.
11 And when they had received it, they complained against the landowner,
12 saying, 'These last men have worked only one hour, and you made them equal to us who have borne the burden and the heat of the day.'
13 But he answered one of them and said, 'Friend, I am doing you no wrong. Did you not agree with me for a denarius?
14 Take what is yours and go your way. I wish to give to this last man the same as to you.
15 Is it not lawful for me to do what I wish with my own things? Or is your eye evil because I am good?'
16 So the last will be first, and the first last. For many are called, but few chosen."
Gospel of Matthew, chapter 20 verses 1 to 16