There are many categorizations of the 613 mitzvot, commandments. Perhaps the most common is the division between those commandments that are between Humans and G-d (Bein Adam Lamakom) and those which are interpersonal- between people (Bein Adam Lachavero).
There is no distinction between the 2 in regard to importance. Living a true Torah life requires one to be aware of and careful in the performance of commandments without regard with whom (or Whom) we are interacting.
This principle of faith is underscored in Parshat Naso:
“‘דבר אל בני ישראל איש או אשה כי יעשו מכל חטאת האדם למעל מעל בה’ ”
“Speak to the children of Israel: When a man or woman commits any of the sins against man to act treacherously against God.”
This refers to one who steals or withholds money from another. While such an act would be a severe trespass of a mitzvah Bein Adom Lachavero (and it is), it is also called a “treachery against G-d”.
Taking from others or denying them their due is as much a sin against G-d Himself as it is against people. It as if he or she is challenging what G-d has decided to bestow on another.
This idea, however, is not limited to matters of money. The wording is clear. One who commits any of the sins against another is being treacherous towards HaShem.
Our purpose in this world to make it a better place through our observance of the entire Torah. In addition to our duties to G-d, we must coexist with others, be it our relatives, friends, neighbors or strangers. The Mitzvot Bein Adom Lachavero sanctify that coexistence.
A Godly person is one who works for excellence in all of his/ her actions. Shabbat, Kashrut, Prayer, etc. are no more important than honesty, integrity, kindness and compassion (to name but a few).
While sinning against G-d is terrible, it is called just that, a sin. When the infraction is toward another person, it becomes treachery against G-d.
There is a common thread throughout the events of the parsha- relationships. Different types of relationships on all levels. Between the tribe of Levi and HaShem/the nation, husband and wife, between people and their Creator, between the mundane and the holy, and between each other.
The message is clear. No matter what or with whom the relationship is, we should strive to make it the best, and holiest, it can be.