The word katischuō = “prevail against”] may mean:
- the gates of hades will not be able to hold out against the Church when the Church assaults it
- the gates of hades will not be able to overcome the Church when the Church is assaulted
**So: **
- is the Church under attack
- or attacking
- **or is one or other meant depending on the circumstances ? **
ISTM that the text is meant to mean both. What is not in doubt, is the final result: whatever happens, the "gates of hades" (hades is the word used here, FWIW) are not going to overcome: the result is a foregone conclusion. (like other acts of God - which is not an excuse for Christians to laze about.)
That’s not the end of it though - for, while the final result is certain, there is nothing to say, in the immediate text, or anywhere else in the Bible, that the "gates of hades" won’t “prevail” in some of the battles of the war. Certainty of final victory is perfectly compatible with many heavy defeats in the meantime. In the war against Hannibal (218-202 B.C.), the Romans were (at least militarily) the victors - but not before some disastrous defeats, as at Trasimene (217) & Cannae (216) - they lost 130,000 men in those two battles alone. But they won the war. Or take the two World Wars - tens of millions died on both sides;
**not on the losing aside alone. **
**So ISTM that the Church is given no guarantee of unfailing victory in all battles - I don’t see any hint of this anywhere: if it is were so, ISTM it would be a bonus; but in view of the terrible evils & many disasters that have happened, not to mention the less spectacular but no less evil wrongdoing that is known only to a few or to God, it is very hard to see how that interpretation can be squared with what has happened. OTOH, it can be squared with an interpretation that sees in His words a promise of final victory despite all evils until then. **
**If there were not many evils in the Church & in Christians, He would not be able to be seen as victorious over them - they serve His Purposes, despite those who do them. He cannnot be thwarted, & this incident may be an application of that. If so, it is a preparation for His decisive victory won on the Cross over hell & its powers. ****It is after all His Church (not ours) & His Faithfulness (not ours) that is its mainstay - it would not be able to endure one moment, without Him as its Strength. **