expression, adverb
for oneself; for one's own sake; on one's own account
Expresses doing something for one's own benefit, purpose, or interest. Often used adverbially to modify a verb.
See also: 為に
自分のために勉強する。
I study for my own sake.
彼は自分のために貯金している。
He is saving money for himself.
Compound of 自分 (self) + の (possessive particle) + 為 (sake, benefit) + に (adverbial particle). The phrase is transparently derived from its components.