Syntactic Structure
Clause A — Subject
ὁ κλέπτης — the thief
↳ Verb
οὐκ ἔρχεται — does not come (present middle/deponent indicative)
↳ Exception
εἰ μή — except, unless
↳ ἵνα Clause (purpose)
ἵνα κλέψῃ καὶ θύσῃ καὶ ἀπολέσῃ — to steal, kill, and destroy
Clause B — Subject
ἐγώ — I (emphatic)
↳ Verb
ἦλθον — I came (second aorist active indicative)
↳ ἵνα Clause (purpose)
ἵνα ζωὴν ἔχωσιν — so that they may have life
↳ Amplification
καὶ περισσὸν ἔχωσιν — and have it abundantly