Having a foundation in Christ is vital for all personal relationships. Those who are serious about following Christ can and do look to the scriptures to get themselves through difficult, interpersonal, matters. When only one person has a foundation in Christ and the other does not, on what "foundation" is their relationship? The answer is - there is no foundation. As the Bible would describe, such a "foundation" is built on sand, which is no foundation at all.
Matthew 7:24-27
24 “Therefore everyone who hears these words of mine and puts them into practice is like a wise man who built his house on the rock. 25 The rain came down, the streams rose, and the winds blew and beat against that house; yet it did not fall, because it had its foundation on the rock. 26 But everyone who hears these words of mine and does not put them into practice is like a foolish man who built his house on sand. 27 The rain came down, the streams rose, and the winds blew and beat against that house, and it fell with a great crash.”
Matthew 7:24-27
24 “Therefore everyone who hears these words of mine and puts them into practice is like a wise man who built his house on the rock. 25 The rain came down, the streams rose, and the winds blew and beat against that house; yet it did not fall, because it had its foundation on the rock. 26 But everyone who hears these words of mine and does not put them into practice is like a foolish man who built his house on sand. 27 The rain came down, the streams rose, and the winds blew and beat against that house, and it fell with a great crash.”