Now, to be thoroughly in act is human perfection; in other words, it is to be thoroughly made. According to Catholic theology, perfection demands a substantial transformation, which is called first sanctifying grace and then beatitude; it involves the mysterious co-working of grace and free will. To go into this question further would be a digression. What I want to emphasize is that for Hopkins life was a continuous substantial progress toward perfection. He believed this, he lived this, this is what he wrote. (…) Hopkins’s rhythms, even when he’s not writing sprung rhythm, have the effect of a hyperthyroid injection.
Robert Lowell on Gerard Manley Hopkins (“Hopkins’s Sanctity”, in his indispensable Collected Prose (ed. R. Giroux))