A.T. Robertson Commentary Matthew 18:8

"And if thy hand or thy foot causeth thee to stumble, cut it off, and cast it from thee: it is good for thee to enter into life maimed or halt, rather than having two hands or two feet to be cast into the eternal fire." — Matthew 18:8 (ASV)

In verses 8 and 9 we have one of the dualities or doublets in Matthew (5:29-30). Jesus repeated his pungent sayings many times. Instead of εις γεενναν (5:29) we have εις το πυρ το αιωνιον and at the end of verse 9 του πυρος is added to την γεενναν. This is the first use in Matthew of αιωνιος. We have it again in 19:16,29 with ζοη, in 25:41 with πυρ, in 25:46 with κολασιν and ζοην. The word means ageless, without beginning or end as of God (Romans 16:26), without beginning as in Ro 16:25, without end as here and often. The effort to make it mean "αεονιαν" fire will make it mean "αεονιαν" life also. If the punishment is limited, ipso facto the life is shortened. In verse 9 also μονοφθαλμον occurs. It is an Ionic compound in Herodotus that is condemned by the Atticists, but it is revived in the vernacular Koine. Literally one-eyed. Here only and Mr 9:47 in the New Testament.