If you have a creek that flows through your property that you absolutely appreciate and want to clean the water that runs through it, it would be wise to first clean the head waters that are not on your property. If the water that comes in is clean, that means the water on your property will be cleaner. If you care for that which is first, second things are cared for better.
It’s a rough analogy, but that is kind of what Jesus was talking about when He said, very bluntly, “He who loves (mother, father, son, daughter . . . ) more than Me is not worthy of Me.” (Matthew 10:37). Very often someone will say that they find it difficult to love God more than a spouse or child as if by loving God first, their loved one is loved less. This is not the case. In fact, it is the opposite.
God is not a source of love. God IS love itself. He is the river and source of all love that flows into your life. Although we say that there are different kinds of love, there is not. There is only one love and it comes from God. There are different appropriate expressions of it, but there is only one love. If we love God first, second persons are not loved less but are loved more in keeping with their nature - they are loved better and more fully.
Placing all of one’s hopes of being loved, of being cared for, of being protected and appreciated on a human person is too much for any human to bear. It is hanging a hat on a hook that cannot support the weight. That weight is to be borne by God. Placing it entirely on another human person leaves us extremely vulnerable to disappointment or devastation.
Building first on the love of God takes an extreme pressure off of a relationship and leaves both far less vulnerable. It helps give them the security of being loved while not taxing each other for a sense of self worth and dignity. That all flows from upstream, purifying the waters of love and making it far easier to tend to.
Our faith is not just about following a bunch of rules, it is about discovering how we thrive best. As creatures we have certain conditions in which we flourish. Loving God first is one of those ways in which human relationships grow to their potential. Cutting God out of that process or making it secondary is placing true love on a back burner in favor of something less worthy and effective. Unknowing, perhaps, they want less than God.