A promise is always an important thing. But an oath is not just an ordinary promise. An oath is a promise made in such a way as to accentuate its importance, and to make it binding, as much as is possible to do.
An oath has been defined thus:
"Invocation of a supernatural or holy being called to verify the veracity of a statement... An oath was a special appeal, an expression of sincerity backed up by the threat of divine retribution should the uttering prove false--hence the term 'oath-breaker '. An oathbreaker was assumed to have committed a crime against God or of some divine entity, which would lead to damnation or another form of severe penalty."
A PROMISE MADE TO GOD
A connection is explicitly made between the promise (relating to earthly matters) and the sacred realm. The promise is thus made a sacred thing. The result is that nothing can legitimately overrule the promise. It is stated in an unequivocal way-- unequivocal, literally, in that there is no other "voice" that can equal, let alone supplant, the voice of the promise.
That is a part of the background for the "oath of office" which every member of the United States Congress takes.
A TREASONOUS OFFENSE
And of the oath of office, it is said:
"Oaths of office are usually a statement of loyalty to a constitution or other legal text, as well as an oath to the state or religion the office holder will be serving. It is often considered a treasonous or highly illegal offense to betray one's oath of office."
"A treasonous or highly illegal offense..." Taking this oath is supposed to be no small thing.
'"I do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter: So help me God."'
PLEDGING TO DO ONE 'S UTMOST, EVEN AT THE COST OF ONE 'S LIFE