Those words are from the late Cardinal Van Thuan, the Vietnamese bishop who endured 13 years in prison, 9 of them in solitary confinement. He was arrested simply because he was a priest and bishop.
In his book, Testimony of Hope, he relates how he felt so desolate in prison because he couldn't do anything for the people of his diocese. He had been forced to abandon his people and this broke his heart. But he relates:
"One night, from the depths of my heart, a voice said to me, 'Why do you torment yourself like this? You must distinguish between God and the works of God. Everything you have done and desire to continue doing--pastoral visits, formation of seminarians, of men and women religious, of the laity, of the youth....all of these are excellent works. These are God's works, but they are not God! If God wants you to leave all of these works, do it right away and have faith in him! God can do things infinitely better than you can.... You have chosen God alone, not his works!'"
He said that gave him peace and changed his way of thinking. It's a lot like the kind of active indifference that St. Ignatius recommends. When we have to do discern what God is calling us to, Ignatius says to approach it by being indifferent to the outcome, wanting only what God wants. "Choose God, not the works of God."