Both our relationship with God and our relationships with people are blocked and marred by sin. God potentially fixed our relationship with Him by sending His Son to die for us. After that, its only a matter of repenting of our sins (i.e., turning away; wanting nothing more to do with it; hating it and being repulsed by it); submitting and surrendering ourself to Him (i.e., turning our life over to Him...in other words, dying to self...this begins with coming to Christ in childlike faith, trust and simplicity; humbling ourself before Him; giving ourself fully to Him, as clay gives itself to the potter), and allowing Him to forgive us, through the sacrificial death of His Son, Christ Jesus; and then, walking with Him and getting to know Him better and better in intimate, personal relationship; and serving Him forever. Though we have offended Him, there is no offense on His part, because He is sinless and holy.
However, when it comes to people, both we and other people are sinners, and are imperfect. And both we and other people have caused offenses against each other. So, rather than a sinner being reconciled to a holy God, when it comes to our dealing with other people, its a matter of a sinner being reconciled (or trying to get along with) another sinner. This makes it more difficult for both parties. Fortunately, however, that aforementioned holy God helps us and empowers us to get along with other sinners.
Relationships are everything. In fact, the Ten Commandments are based on relationships.
First, relationship between us and God. Secondly, relationship between us and other people. If we got both of those perfectly right every second of our life (including our thinking, our attitude and our intentions), we would never sin.