From syn (together with) + kathizō (to sit). Synkathizō means to sit down together with, to be seated together. Appears only twice in the NT — Ephesians 2:6 and Luke 22:55 — marking the profound spiritual position of believers and the mundane positioning of those who warmed themselves at the fire the night Jesus was arrested.
The two appearances of synkathizō in the NT form one of the most striking contrasts in Scripture. Luke 22:55: After Jesus' arrest, Peter 'sat down (synkathisantōn) with' those warming themselves at the fire in the high priest's courtyard — the prelude to his threefold denial. Ephesians 2:6: God 'raised us up with Christ and seated us (synekathisen) with him in the heavenly realms.' The same compound verb — but what a difference! Peter synkathizō-ing with the enemies of Jesus at a charcoal fire, versus believers synkathizō-ing with Christ in the heavenly places. The contrast is the gospel itself: the one who denied and sat with enemies is now, by grace, raised and seated with the One he denied. Positional theology — the believer's seating 'in heavenly places' — is not a future promise but a present reality (present tense in the Greek of Eph. 1:3; 2:6). Our standing before God is determined not by our performance but by our union with Christ in His resurrection and ascension.