In one of many letters to a woman who lived in Virginia (the "lady" of Letters to an American Lady), C. S. Lewis in 1958 answered some questions about prayer. At one point he says:
Joy tells me that once, years ago, she was haunted one morning by a feeling that God wanted something of her, a persistent pressure like the nag of a neglected duty. And till mid-morning she kept on wondering what it was. But the moment she stopped worrying, the answer came through as plain as a spoken voice. It was 'I don't want you to do anything. I want to give you something': and immediately her heart was full of peace and delight. St. Augustine says 'God gives where he finds empty hands.' A man whose hands are full of parcels can't receive a gift. Perhaps these parcels are not always sins or earthly cares, but sometimes our own fussy attempts to worship Him in our way.
--The Collected Letters of C. S. Lewis, 3:930-31