Seventy percent of Americans with a religious affiliation say that many religions — not just their own — can lead to eternal life.
This result was derived by the Pew Survey from a forced choice of two statements presented to those who had said they had a religion: My religion is the one, true faith leading to eternal life, or Many religions can lead to eternal life.
For Christians, choosing the second choice is mere Christianity, consistent with the greatest 20th century Christian apologist C. S. Lewis. Children who have read the Narnia series will have learned in The Last Battle that the pagan Calormene soldier was credited with worshiping Aslan all along even though he did not know it.
Lewis also stated this more explicitly in Mere Christianity on page 64:
But the truth is God has not told us what His arrangements about the other people are. We do know that no man can be saved except through Christ; we do not know that only those that who know Him can be saved through Him.
and on page 209:
There are people in other religions who are being led by God's secret influence to concentrate on those parts of their religion which are in agreement with Christianity, and who thus belong to Christ without knowing it. For example, a Buddhist of good will may be led to concentrate more and more on the Buddhist teaching about mercy and to leave in the background (though he might say he still believed) the Buddhist teaching on certain other points.