The parable in Matthew 20:1-16 is another parable in which Jesus Christ teaches us that his kingdom does not operate on the principle of human merit - it is not a performance-based regime.
As Romans 3:21-24 teaches, there is no difference: all of us are equally sinners, and all who are accepted by God are accepted on one basis only - the basis of the righteousness of Jesus Christ, freely given by God's sheer grace. Because of this no one can boast of their relationship with God as if it depended on some quality or merit of their own.
Here in this parable men thought that because they had worked longer they would merit more pay than the agreed day's wage. The employer, however, chose to pay those who had worked for only the last hour of the day the full day's pay. This was his choice. This was his right. This was his pleasure.
It didn't sit well with the all-day workers. Viewing life through self-centred, tit-for-tat, performance-based perceptions they cared only for themselves and criticized their employer. They could not rejoice with their fellow employees who had benefited from the employer's generosity and grace; they could not appreciate the employer's compassion which responded to real needs rather than to perceived merit.
Their greatest loss was not their perceived loss of income but their utter failure to appreciate their employer's value system.
Even so do we suffer loss when we live by the principle of performance, despising the principle of grace. God's choice, God's pleasure, God's way - the operating principle of his kingdom - is grace: incomparable, unsearchable, lavished upon us in Jesus Christ.
In this the Christian rejoices. In this the Christian trusts. In this there is perfect peace and perfect assurance.
Scriptures: Matthew 20:1-16; Romans 3:19-28; Ephesians 1:6,7; 2:7; 3:8; Philippians 3:1-11; Romans 5:1; 4:16; 2 Timothy 1:12.