The answer to your good question is full of conjecture. Let’s look at a few of the sins mentioned in the Bible. You may think of something different that what I put forward, but I think we can all agree that ALL sin is bad.

Genesis 3:6, “And when the woman saw that the tree was good for food, and that it was pleasant to the eyes, and a tree to be desired to make one wise, she took of the fruit thereof, and did eat, and gave also unto her husband with her; and he did eat.” The is the first sin that man ever committed and it plunged the whole world into darkness. Sin is disobedience and Adam and Eve disobeyed God by eating of the forbidden fruit. We read in Romans 5:12, “Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned.” The consequence of this sin is still being felt by all today.

Genesis 4:8, “And Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him.” Most will remember how that Cain and Abel both made offerings to the Lord. Abel’s offering of the ‘firstlings of his flock’ was accepted of the Lord while Cain’s offering of ‘the fruit of the ground’ was not accepted of the Lord. In a jealous rage, Cain killed his brother. How tragic to see that the first man every born was also the first murdered in history.

Numbers 20:7-12, “And the LORD spake unto Moses, saying, Take the rod, and gather thou the assembly together, thou, and Aaron thy brother, and speak ye unto the rock before their eyes; and it shall give forth his water, and thou shalt bring forth to them water out of the rock: so thou shalt give the congregation and their beasts drink. And Moses took the rod from before the LORD, as he commanded him. And Moses and Aaron gathered the congregation together before the rock, and he said unto them, Hear now, ye rebels; must we fetch you water out of this rock? And Moses lifted up his hand, and with his rod he smote the rock twice: and the water came out abundantly, and the congregation drank, and their beasts also. And the LORD spake unto Moses and Aaron, Because ye believed me not, to sanctify me in the eyes of the children of Israel, therefore ye shall not bring this congregation into the land which I have given them.” Still in the wilderness between Egypt and Canaan, the Lord’s people murmured because of a lack of water. The Lord instructed Moses to speak to a particular rock in the presence of the people and He would provide water. Moses grew angry at the people and hit the rock, rather than speaking to it. For his act of disobedience, Moses was not allowed to take God’s people into the promised land.

Matthew 2:16, “Then Herod, when he saw that he was mocked of the wise men, was exceeding wroth, and sent forth, and slew all the children that were in Bethlehem, and in all the coasts thereof, from two years old and under, according to the time which he had diligently inquired of the wise men.” Trying to kill this pronounced ‘king of the Jews’, King Herod had all the children in Bethlehem, up to two years of age, killed. What a tragic event.

Moses was a murderer (Exodus 2:11-12). Rahab was a prostitute (Joshua 12:1). Rebekah was a liar (Genesis 27:1-17). Onesimus was a runaway slave and a thief. (Philemon 1:15-18). According to the Apostle Paul, he was the greatest sinner who ever lived. In 1 Timothy 1:15 he stated, “This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief.” The list goes on and on.

What is the greatest sin mentioned in the Bible? It would have to be anyone that rejected the call of God’s grace and did not put their faith in the Lord Jesus Christ. To pass into a lost eternity is the greatest of all sin for it will doom the sinner to an eternity of the wrath of God. Of unrepentant sinners, it is said in Matthew 25:46, “And these shall go away into everlasting punishment…” Some sins appear to be relatively small, some are large and obviously illegal. ANY sin will prevent us from going to Heaven. And we have all sinned (Romans 3:23). Yet, there is hope for ALL sinners. We read in Romans 6:23, “For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.” Have you accepted God’s gift of eternal life by putting your faith in the Lord Jesus Christ as your Lord and savior? (338.2)