If there is no salvation outside the Church, then what relationship does Christ’s sacrifice on the cross have with those who sincerely believe in a false religion and die having never entered the Church?
Remember that Jesus said from the cross, “Father, forgive them; for they know not what they do” (Lk 23:34). What did his sacrifice on the cross have to do with those who mocked him, spit at him, and crucified him? In other words, what did it have to do with those for whom he was asking forgiveness from God the Father? The answer is: everything. For some, it was through ignorance that they crucified him, and invincible ignorance can diminish one’s culpability for evil done—even the crucifixion of our Savior.
They still could be saved, or Jesus’ plea for their forgiveness to the Father would make no sense. Whoever enters heaven will do so only because of Christ and his sacrificial work on the cross. Some people may enter heaven having never heard of Christ, but it will be because of him that they enter.