Because narrow is the gate and difficult is the way which leads to life, and there are few who find it.
As a Christian I often wonder what exactly is the fate of “the innocent native”. The one who has never heard Christ. Or on the other hand, the one who though struggling and groping toward Something is not Christian because of us Christians.
It is not to me an abstract problem. I know people like this. People who look at Christianity and reject it, not because of its message but because of its practice. And who can blame them? I very nearly did the same. But they know there is a transcendent Truth. Something greater and above them. They seek it, but lacking the Light of Christ they can only go so far.
And then I read this verse. One which has hitherto seemed an exclusionary verse. But I realized that what seems to be required of humanity here is not that we reach the gate, but that we struggle along the road. It is possible, though of course I am no theologian and ill suited for speculation on such things, that what matters is not entirely that we reach the gate but that we are trying with all our might to reach the gate. If all our energies are devoted to God, though we know Him not for Who He truly is, then I think it is possible that one can attain salvation; though again I can only speculate and that poorly.
If at the end of our life we have only found the narrow way and are still far from the gate, I do not know that God will not carry us the rest of the way.