Reflexive pronoun used for emphasis or to refer back to a previously mentioned inanimate or animate entity. Often contrasts with other entities or highlights the thing in question.
See also: 彼女自身 (かのじょじしん)
The problem is not difficult in itself; it's that there isn't enough time.
He didn't blame himself for that.
彼自身 is specifically 'himself' for a male person, whereas それ自身 can refer to inanimate objects or be used more abstractly.
Standard modern spelling.
Archaic kanji form using 其れ; rarely used in contemporary writing.
Compound of それ (that) and 自身 (self). The form follows the pattern of personal pronoun + 自身 to create a reflexive pronoun.