If a man vow a vow. נֶדֶר, a vow, is commonly said to be distinctively a positive vow, a promise to render something unto the Lord. This, however, cannot be strictly maintained, because the Nazarite vow was healer, and that was essentially a vow of abstinence.
To say that the vow of the Nazarite was of a positive character because he had to let his hair grow "unto the Lord" is a mere evasion. It is, however, probable that neder, when it occurs (as in this passage) in connection with issar, does take on the narrower signification of a positive vow.
Swear an oath to bind his soul with a bond. Literally, "to bind a bond upon his soul." אִסָּר, a bond, which occurs only in this chapter, is considered to be a restrictive obligation, a vow of abstinence.
It would appear that the issar was always undertaken upon oath, whereas the neder (as in the case of the Nazarite) did not of necessity require it. He shall not break his word. This was the general principle with respect to vows, and, as here ]aid down, it was in accordance with the universal religious feeling of mankind.
Whatever crimes may have claimed the sanction of this sentiment, whatever exceptions and safeguards a clearer revelation and a better knowledge of God may have established, yet the principle remained that whatsoever a man had promised unto the Lord, that he must fulfill.
Iphigenia in Aulis, Jephthah's daughter in Gilead, proclaim to what horrid extremities any one religious principle, unchecked by other coordinate principles, may lead; but they also proclaim how deep and true this religious principle must have been which could so over-ride the natural feelings of men not cruel nor depraved.