“He moved into marriage with an imminent expectation of death, in an extraordinary witness of love and courage and personal sacrifice.” 

Madeleine L’Engle is describing Lewis’s decision to marry Helen after she was diagnosed with terminal cancer. She observes that the unusual circumstances created a different emotional dynamic than occurs in more typical marriages.

“It tells of the agony and the emptiness of a grief such as few of us have to bear, for the greater the love, the greater the grief, and the stronger the faith the more savagely will Satan storm its fortress.” 

Douglas Gresham is describing and summarizing A Grief Observed from his perspective of witnessing the relationship between his mother and Lewis, and also living with Lewis, after his mother died.

“No one ever told me that grief felt so like fear. I am not afraid, but the sensation is like being afraid.” 

This is the first sentence of A Grief Observed. Lewis, in the immediate aftermath of his wife’s death, is describing the shock he experienced in the initial stage of grief. Lewis observes that he still experiences feeling grief as fear in later chapters of the book.