67:1 A person should not get in the habit of making vows. (Vow = neder in Hebrew.) One who makes a vow is considered as if he built a bamah (a private altar) after making such altars became prohibited (i.e., a misguided attempt at doing something meritorious). When he fulfills the vow, it is as if he offered a sacrifice on this bamah, which violates the prohibition against sacrificing animals outside the Temple. If one did make a vow, it is preferable to attempt to have it annulled. All this only applies to vows of a general nature but if one made a vow sanctifying something to the Temple, it is a mitzvah to fulfill his obligation as per Psalms 116:14, “My vows to G-d, I will fulfill.” These vows should only be annulled in compelling circumstances.
67:2 A person should likewise avoid making oaths. (Oath = shavua in Hebrew.) If a person did swear an oath, he should not try to get out of it. Rather, he should keep the oath even if it is difficult, as per Psalms 15:4, “A person who swears to his own detriment and does not change it...” which is followed by “Those who do these things will never stumble” (15:5). One should attempt to be absolved of an oath only in compelling circumstances.