The love between brother and sister differs from the love between man and wife in three respects. Unlike marital love, fraternal love does not depend upon physical proximity. Fraternal love is relatively constant, whereas the intensity of marital love fluctuates. Fraternal love is cold, lacking passion, while marital love is fiery and impassioned. The root of these distinctions is that the love between brother and sister is instinctive and natural, requiring no arousal other than memory, while the love between husband and wife is a continually new experience of closeness.
The first stage in the soul's relationship to G-d is compared to the love between sister and brother. It is a love which has the advantages of being instinctive, natural and constantly present. This love is not a burning passion, a desire to thrust oneself into the unity of G-d; nevertheless, a Jew must first reach this stage of awareness in his "arousal from below". This stage is non-wavering and requires no additional state of consciousness to one's simple, eternal Jewish identity. Possessed by every Jew, this love is a hereditary instinct, transmitted to us from our forefathers, Abraham, Isaac and Jacob. It can be expressed from afar and does not depend upon deep religious experiences, which are not usually present in the first stages of serving G-d.