The rabbis discuss the dangers of a man marrying a woman of the heathen nations, and Abraham's desire that Isaac remain in the Central Column, where he would learn the ways of the Holy One.
This pertains to the importance of our relationships in life, including their effect on the spiritual state of things. Marriage is the union of two halves of one soul, and is considered an important tool for drawing the Light of the upper worlds [husband] into the lower world [wife]. All our actions in this material realm, including marital transactions, are a microcosm of the ebb-and-flow relationship endlessly playing out between the physical and metaphysical worlds. To secure a personal connection to the macrocosmic level of reality, thus ensuring its positive influence in our life, we must surround ourselves with those in whom the love of the Creator burns strongly, rather than those whose godlessness seeks to infect us with unbelief. Consciousness creates reality. People who are not conscious of the Creator create for themselves a Godless reality devoid of spiritual Light. Whether in business, social, or marital relationships, the Zohar helps prevent us from becoming entangled with negative partners, and to attract like-minded, virtuous people into our life.