Ezekiel prophesied against the secular and religious leaders in Israel, who had been fattening their bank accounts by exploiting those they were supposed to be serving (Ez 34:3ff). As a result, the people suffered brutally, while the "shepherds" profited. Similar events still occur today. For example, it's not unusual to see a CEO walking away with a multimillion dollar settlement while leaving his former company in ruins and many of his former employees out of work.
It's easy to see the crass exploitation in these examples. In contrast, in today's Gospel, Jesus addresses those who worked hard for Him all day (Mt 20:12). At the end of the day, they were focused on what they would get, not what Jesus would get (Mt 20:10). Despite working for God, they were "busy seeking [their] own interests rather than those of Christ Jesus" (Phil 2:20). Jesus the Good Shepherd (Jn 10:14) calls both bad and good shepherds to repentance and greater maturity.
Often working for Jesus involves working "a full day in the scorching heat" of God's vineyard (Mt 20:12). Fulfilling your call to shepherd those He has entrusted to your care can be "a great contest of suffering" (Heb 10:32). When you suffer for God's sake, "it is a test for you, but it should not catch you off guard" (1 Pt 4:12). God's will is that you rejoice when you suffer for Him (1 Pt 4:13; Col 1:24).
Give a wholehearted "Yes" to Jesus' invitation to work in God's vineyard. Let the Good Shepherd use you, and use you up.