The Greek preposition anti means instead of, in place of, on behalf of, or in exchange for. Its core meaning is substitution or correspondence — one thing in the place of another. It occurs about 22 times in the New Testament and is theologically crucial in the concept of substitutionary atonement.
Anti is the preposition embedded in the Greek word for 'ransom' (antilutron, 1 Timothy 2:6) and in the logion of Jesus: 'the Son of Man came not to be served but to serve, and to give his life as a ransom for many' (Matthew 20:28 — lutron anti pollōn). The substitutionary force of anti undergirds the entire atonement theology of the New Testament — Christ dying 'in the place of' sinners. Hebrews 12:2 says Jesus endured the cross 'for the joy set before him' (anti tēs... charas) — enduring the cross in exchange for eschatological joy. The preposition small as it is contains the architecture of the Gospel.