Maulana Wahiduddin Khan | Discover Islam | Al-Risala, May 1987, p. 10
It is stated in the Quran: “If anyone seeks a religion other than Islam [submission to God], it will not be accepted from him; he will be among the losers in the Hereafter.” (3: 85)
The usual explanation of this verse is that Islam will become a means of salvation in the Hereafter because it is a complete religion; its Prophet is the greatest of all the Prophets; its Scripture is the most sacred of all the Scriptures. But this is not consistent with what is said in the Quran and is little better than a weak argument in favour of a strong point. It also contradicts the saying, which appears in several places in the Quran, that “God does not wrong His servants in the slightest.” It contradicts it, because it would have us believe that God had discriminated between different sets of human beings, in giving to those who lived before the Final Prophet an inferior religion and to those who came afterwards a superior religion. Such an allegation cannot be laid at God’s door. It is contrary to God’s nature that he should discriminate between his creatures in the bestowing of His mercy.
The true reason for Islam being the sole way to salvation is that it is the one and only religion preserved in its original form. In their own times, previous religions were just as valid as Islam is today. But the scriptures of other religions were tampered with. Their adherents interpolated and deleted at will. This having happened, these scriptures ceased to be authentic sources for the understanding of the Will of God. This is the sole reason that other religions fell by the wayside in later times, and that Islam alone survives as the one source of True Guidance.