With this in mind let us attack the passage.
The landowner employs labourers in a vineyard for an agreed and just wage. As he has need for more labourers later in the day, he employs them also. He pays the latecomers first and they get the same agreed and just wage as the early starters. This causes grumbling. The Punch line is this: Have I no right to do what I like with what I own? Why be envious because I am generous?
The application of a parable is left to the listener. Here, Jesus is talking to his disciples. He is telling them that their long standing contract with God and His chosen people is a faithfully fulfilled contract on God’s part. The agreed wage will be paid. But they should not be envious of the gentiles who are coming into the kingdom at a later date. God is generous. God is fair.
This is the meaning of “Thus the last will be first and the first will be last”. There is a subtle warning in the parable to the scribes and Pharisees and to all of us. Seniority does not ensue privilege. It does ensue justice. And justice is administered by a generous God according to His plan!!!!!