To cooperate means literally to work together.
As Father William reminded us in his Sunday homily, God's desire is meant to be received and echoed by our desire to do his will. We must choose to follow our deepest desires, those longings for the Good and the True that persistently arise in the depths of our hearts, planted there by the Holy Spirit. God speaks to us through these deepest desires, as they are discerned to be consonant with Sacred Scripture, the Church's Tradition and teaching and our abilities and our prayer. Then, as Peter Kreeft will say, we must test our choice "by holding it before God."
Vintage image from Our Lady of the Valley, the monastery from which our Abbey was founded.