Heneka (ἕνεκα, also heneken or heineken) is a causal/purposive preposition meaning 'for the sake of,' 'on account of,' or 'because of.' It introduces the reason or motivation behind an action — what someone suffers, does, or acts for.
The most theologically significant use is in the beatitudes: 'Blessed are those who are persecuted for righteousness' sake (heneka dikaiosynes) — (Matthew 5:10) — and 'Blessed are you when others revile you... on my account (heneken emou)' (Matthew 5:11). Suffering heneka — for the sake of Christ and righteousness — is declared blessed. Romans 8:36 quotes Psalm 44:22: 'For your sake (heneka sou) we are being killed all day long.' Paul's catalog of sufferings (2 Corinthians 12:10) is explicitly framed as suffering 'for Christ's sake' (huper Christou and heneka). The preposition transforms the meaning of suffering: what is endured for whom defines its value.
The preposition heneka asks every Christian the decisive question: for whose sake? Suffering for one's own failures is merely consequence; suffering for Christ's sake is participation in the paschal mystery. Paul reframes his entire catalog of weaknesses and sufferings as suffering heneka Christou (for Christ's sake, 2 Corinthians 12:10) — which is why he can say he is 'content' in them. The reason behind the suffering transforms its meaning entirely.