The quote is from the late, saintly Cardinal van Thuan. He suffered for 13 years in Communist prisons in North Vietnam, including many years in solitary confinement. Once he was regretting how he was unable to carry out his ministry for his people. Suddenly in his heart he heard the words, "Seek God, not the works of God." He realized he was feeling bad because he couldn't do works for God. But God was telling him that he didn't need those works; he needed to seek God.
I like to think about it on those days when it seems like frustrations bedevil everything I do! God doesn't need me to do great works. He needs me to love him and his people.