“For the kingdom of heaven is like a master of a house who went out early in the morning to hire laborers for his vineyard. After agreeing with the laborers for a denarius a day, he sent them into his vineyard. And going out about the third hour he saw others standing idle in the marketplace, and to them he said, ‘You go into the vineyard too, and whatever is right I will give you.’ So they went. Going out again about the sixth hour and the ninth hour, he did the same. And about the eleventh hour he went out and found others standing. And he said to them, ‘Why do you stand here idle all day?’ They said to him, ‘Because no one has hired us.’ He said to them, ‘You go into the vineyard too.’ And when evening came, the owner of the vineyard said to his foreman, ‘Call the laborers and pay them their wages, beginning with the last, up to the first.’ And when those hired about the eleventh hour came, each of them received a denarius. Now when those hired first came, they thought they would receive more, but each of them also received a denarius. And on receiving it they grumbled at the master of the house, saying, ‘These last worked only one hour, and you have made them equal to us who have borne the burden of the day and the scorching heat.’ But he replied to one of them, ‘Friend, I am doing you no wrong. Did you not agree with me for a denarius? Take what belongs to you and go. I choose to give to this last worker as I give to you. Am I not allowed to do what I choose with what belongs to me? Or do you begrudge my generosity?’ So the last will be first, and the first last.” (Matthew 20:1-16)
The substance of the parable consists not in the penny, what it is, nor in the different hours; but in earning and acquiring, or how one can earn the penny; that as here the first presumed to obtain the penny and even more by their own merit, and yet the last received the same amount because of the goodness of the householder. Thus God will show it is nothing but mercy that he gives and no one is to arrogate to himself more than another. Therefore, he says I do you no wrong, is not the money mine and not yours; if I had given away your property, then you would have reason to murmur; is it not lawful for me to do what I will with mine own?
Now in this way Christ strikes a blow first against the presumption of those who would storm their way into heaven by their good works. These all labor for definite wages, that is, they take the law of God in no other sense than that they should fulfill it by certain defined works for a specified reward, and they never understand it correctly, and know not that before God all is pure grace. This signifies that they hire themselves, out for wages, and agree with the householder for a penny a day; consequently, their lives are bitter and they lead a life that is indeed hard.
Now when the Gospel comes and makes all alike, as Paul teaches in Rom 3:23, so that they who have done great works are no more than public sinners, and must also become sinners and tolerate the saying: All have sinned, and that no one is justified before God by his works; then they look around and despise those who have done nothing at all. Then they murmur against the householder, they imagine it is not right; they blaspheme the Gospel, and become hardened in their ways; then they lose the favor and grace of God, and are obliged to take their temporal reward and trot from him with their penny and be condemned; for they served not for the sake of mercy but for the sake of reward, and they will receive that and nothing more, the others, however, must confess that they have merited neither the penny nor the grace, but more is given to them than they had ever thought was promised to them.
Therefore, if one were to interpret it critically, the penny would have to signify temporal good, and the favor of the householder, eternal life. But the day and the heat we transfer from temporal things to the conscience, so that work-righteous persons do labor long and hard, that is, they do all with a heavy conscience and an unwilling heart, forced and coerced by the law; but the short time or last hours are the light consciences that live blessed lives, led by grace, and that willingly and without being driven by the law.
Therefore, we clearly see, if we look into their hearts, that the last had no regard for their own merit, but enjoyed the goodness of the householder. The first however did not esteem the goodness of the householder, but looked to their own merits, and thought it was theirs by right and murmured about it.
The substance of this Gospel is that no mortal is so high, nor will ever ascend so high, who will not have occasion to fear that be may become the very lowest. On the other hand, no mortal lies so low or can fall so low, to whom the hope is not extended that he may become the highest; because here all human merit is abolished and God's goodness alone is praised.