His intuitions about people were not in fact of a very penetrating character.
His mother appeared to all her world as a "sweet old lady," but even Martin could already perceive that was not in the least what she really was.

He had seen her old hands tremble with suppressed temper on the very day after his arrival; he had seen her old lips white with anger because the maid had brought her the wrong shawl.

Old ladies must of course have their fancies, but his mother had some fixed and fierce purpose in her life that was quite beyond his powers of penetration.

It might of course have something to do with her attachment to his father.
Attached Martin could see that she was, but at the same time completely and eternally outside her husband's spiritual life.

That might have been perhaps in the first place by her own desire--she did not want "to be bothered with all that nonsense." But certainly all these years with him had worked upon her: she was not perhaps so sure now that it was all "nonsense." She wanted, it might be, a closer alliance with him, which she could not have because she had once rejected the chance of it.