In Genesis 4 we find the story of Cain and Able. It gives us the most important principle for guarding and protecting relationships. Cain brought an offering of the fruit of the ground to the Lord, but the Lord did not respect it. God told Cain all he had to do, was to do well and he would be accepted ( v 7). In other words all he had to do was adjust the attitude of his heart, which would change his behaviour and all would be well. There was an issue vertically, between Cain and God. However Cain ignored that and focused horizontally, making it an issue between himself and his brother.
That will always happen. When something unhealthy arises in our hearts, God will have an issue with us. He will lovingly bring our attention to the problem and tell us to adjust. If we ignore our vertical problem with God, it is only a matter of time and there will be a horizontal problem with someone else. The issue between us and God will turn into an issue between us and another person, our spouse, our friend, our child, because something unhealthy in our heart, hasn’t been dealt with.
When we fail to deal with ourselves in a healthy manner, we deal with ourselves in an unhealthy manner, by taking out our mistake on someone else, in the form of anger, revenge, criticism or some other unloving, destructive behaviour.
Vertical trouble, leads to horizontal trouble. If we guard and are sensitive and obedient in our vertical relationship with God, it will guard and protect our horizontal relationships with others.