it is only by an amiable vanity that women ascribe to it spiritual value. 中的by和that怎么分析

But the bed I made up for myself was sufficiently uncomfortable to give me a wakeful night, and I thought a good deal of what the unlucky Dutchman had told me. I was not so much puzzled by Blanche Stroeve's action, for I saw in that merely the result of a physical appeal. I do not suppose she had ever really cared for her husband, and what I had taken for love was no more than the feminine response to caresses and comfort which in the minds of most women passes for it. It is a passive feeling capable of being roused for any object, as the vine can grow on any tree; and the wisdom of the world recognises its strength when it urges a girl to marry the man who wants her with the assurance that love will follow. It is an emotion made up of the satisfaction in security, pride of property, the pleasure of being desired, the gratification of a household, and it is only by an amiable vanity that women ascribe to it spiritual value. It is an emotion which is defenceless against passion. I suspected that Blanche Stroeve's violent dislike of Strickland had in it from the beginning a vague element of sexual attraction.

请教老师：上面节选中，这一句 and it is only by an amiable vanity that women ascribe to it spiritual value. 中的by和that怎么分析？

另外，...had in it中的it是指的an emotion吧？