First things First.

23 So if you are offering your gift at the altar and there remember that your brother has something against you, 24 leave your gift there before the altar and go. First be reconciled to your brother, and then come and offer your gift. (Matthew 5) 
So often, if not always, our vertical relationship with God intertwines with our relationships with others, and each affects the other.  We can never hope to have a fully functional relationship with anyone else - spouse, parent, child, boss, co-worker, etc., unless we first are in right relationship with God.  So why does God here instruct us to make that relationship with another right first? Because He knows how much we want to feel good about ourselves.  We will always do the easiest thing to make ourselves feel better, leaving behind the harder thing which will truly move us to making all things right. It's easier to write a check than give an apology.  Another example is the rich man who wanted to know how to inherit eternal life. He saw doing all the things on the checklist as easier than doing what was hardest for him: letting go of his stuff and giving it away to the poor, and fully trusting God to provide what he needed.  In both of these cases, the instructions are the way to make both the vertical and horizontal relationships right at the same time. So, doing first things first, is really the first step in doing both. What hard thing does God want today?