One could write many pages in answering your questions, but due to space limits I am going to keep this short. Regarding your first question, there actually is a simple answer found very early in man’s history. Let’s read Genesis 4:1-5, “Now Adam knew Eve his wife, and she conceived and bore Cain…then she bore again, this time his brother Abel. Now Abel was a keeper of sheep, but Cain was a tiller of the ground. And in the process of time it came to pass that Cain brought an offering of the fruit of the ground to the LORD. Abel also brought of the firstborn of his flock and of their fat. And the LORD respected Abel and his offering, but He did not respect Cain and his offering” (NKJV). Now let’s read Hebrews 11:4, “By FAITH Abel offered a more EXCELLENT SACRIFICE than Cain, through which he obtained witness that he was righteous.”

Cain was the first man to start a RELIGION that was not of God. He decided to come to God on his own terms; in his thinking God would surely accept his offering (“the fruit of the ground”) that he had worked so hard for (see Genesis 3:17-19). He must have thought, “This is the best offering I could bring to God.” The problem is he was coming (as we shall see) WITHOUT FAITH and WITHOUT THE PROPER SACRIFICE. In short, he was seeking to come to God IN HIS OWN WAY. We read twice in the book of Proverbs, “There is A WAY which seems right to a man, but its end is THE WAY OF DEATH” (14:12; 16:25). Cain’s WAY seemed right to him, yet it leads to DEATH. Romans 6:23 declares, “The wages of sin is death.” In Jude 11 we read, “Woe to them! For they have gone in THE WAY OF CAIN.” Jude was writing of those who in his day were just like Cain; they were RELIGIOUS and seeking to come to God IN THEIR OWN WAY. The religions you referred to in your question are, sad to say, “going in the way of Cain.” They are all trying to reach their version of heaven by good works…without faith and without the proper sacrifice that God will accept. So, instead of going into the history of each of these religions to see exactly how they began, we have exposed the ROOT of their religion. All of them began in the same way as Cain’s religion, by men thinking (in the fertile imaginations of their sinful mind and heart) they could obtain a righteous standing before God (a “God of their own devising”) by their own efforts.

Abel, on the other hand, came to God BY FAITH. Romans 10:17 tells us, “So then faith comes by hearing, and hearing by the word of God.” Abel no doubt had a “word from God” as to what offering he should bring to Him that would be acceptable. Perhaps his parents had told him (and Cain) about their fall into sin (by eating of the forbidden fruit…Genesis 2:15-17 and 3:6), their being naked before God (verse 7), and how God clothed them with the skins of slain animals (verses 20-21). Abel BELIEVED GOD and came to Him with the only sacrifice He can and will accept…the DEATH of an innocent victim whose BLOOD had to be shed. Of course, Abel’s sacrifice looks on to the supreme sacrifice of the Lord Jesus Christ, whose blood was shed on Calvary to take away our sins and to make us righteous in God’s sight (see John 1:29; 19:34; Hebrews 9:12-14, 22-26). This is why Jesus said, “I am THE WAY, the truth, the life, no man comes to the Father but by Me” (John 14:6).

In closing, one has said that “there are but two religions in the world; —the true, that of God’s appointing; the false, the product of man’s own mind. The first is the religion of faith; the second that of credulity or superstition, in whatever form it may appear” (H. A. Ironside). So, in answer to your second question, because all of the religions outside of Christianity are false, the Bible’s position on their religious writings is to reject them. “Beware lest anyone cheat you through philosophy and empty deceit, according to the tradition of men, according to the basic principles of the world, and NOT ACCORDING TO CHRIST” (Colossians 2:8). If someone comes to our door with their false religion, we are to reject them too. “Whoever transgressed and does not abide in the doctrine of Christ does not have God…If anyone comes to you and does not bring this doctrine, do not receive him into your house nor greet him; for he who greets him shares in his evil deeds” (2nd John 9-11).  (360.1)  (DO)