Idolatry: Why it is Considered as the Greatest Sin?

Which is the greatest ruin of a house?
Foundation, because if the foundation give away, immediately the house falls in ruin, in such wise that it is necessary to build it up a new: but if every other part give way it can be repaired. Similarly, idolatry is the greatest sin, because it deprives a man entirely of faith, and consequently of God; so that he can have no spiritual affection. But every other sin leaves to man the hope of obtaining mercy: and therefore idolatry is the greatest sin. 

Idoltary

Remember that which God spoke and which Moses and Joshua wrote in the Law, and you shall see how grave is this sin. God said, speaking to Israel: "You shall not make to yourself any image of those things which are in heaven nor of those things which are under the heaven, nor shall you make it of those things which are above the earth, nor of those which are under the earth; nor of those which are above the water, nor of those which are under the water. For I am your God, strong and jealous, Who will take vengeance for this sin upon the fathers and upon their children even to the fourth generation."

Remember how, when our people had made the calf, and when they had worshiped it, by Commandment of God Joshua and the tribe of Levi took the sword and slew of them one hundred and twenty thousand of those that did not crave mercy of God. 

And God instruct Moses His servant- Now therefore kill every male among the little ones (taph), and kill every woman that hath known man by lying with him. But all the female children (taph), that have not known a man by lying with him, keep alive for yourselves. -[Num. 31:17-18]
Oh, terrible Judgment of God upon the idolaters!"

A Pharisee invited Jesus to supper and he came thither with his disciples. Whereupon, the disciples sat down to table without washing their hands. The scribes called Jesus, saying: "Wherefore do not your disciples observe the traditions of our elders, in not washing their hands before they eat bread?"

He answered: "And I ask you, for what cause have you annulled the precept of God to observe your traditions? You say to the sons of poor fathers: "Offer and make vows to the Temple."

And they make vows of that little wherewith they ought to support their fathers. And when their fathers wish to take money, the sons cry out: "This money is Consecrated to God"; whereby the fathers suffer. 

O false scribes, hypocrites, does God use this money? Assuredly not, for God eats not, as he says by his servant David the prophet: Shall I then eat the flesh of bulls and drink the blood of sheep? Render to me the "Sacrifice of Praise", and offer to me your vows; for if I should be hungry I will not ask aught of you, seeing that all things are in my hands, and the abundance of paradise is with me. Hypocrites! you do this to fill your purse, and therefore you tithe rue and mint.

Oh miserable ones! for to others you show the most clear way, by which you will not go. 'You scribes and doctors lay upon the shoulders of others weights of unbearable weight, but you yourselves the while are not willing to move them with one of your fingers.

Truly, "Every evil has entered into the world under the pretext of the Elders". Tell me, who made idolatry to enter into the world, if not the usage of the elders? 

There was a king who exceedingly loved his father, whose name was Baal. Whereupon, when the father was dead, his son for his Own Consolation, caused to be made an image like to his father, and set it up in the market-place of the city. And he made a decree that every one who approached that statue within a space of fifteen cubits should be safe, and no one any account should do him hurt.

Hence the Malefactors, by reason of the benefit they received therefrom, began to offer to the statue Roses and Flowers, and in a short time the offerings were changed into Money and Food, insomuch that they called it god, to honour it.

Which thing from custom was transformed into a law, insomuch that the idol of Baal spread through all over the world; and how much does God Lament this by the Prophet Isaiah, saying: "Truly this people worships Me in vain, for they have annulled My Law given to them by My servant Moses, and follow the traditions of their elders.’

Truly I say to you, that to eat bread with unclean hands defiles not a man, because that which enters into the man, defiles not the man, but that which comes out of the man defiles the man."

Thereupon, one of the scribes asked: "If I shall eat pork, or other unclean meats, will they not defile my conscience?" 

"Eating Pork is directly disobedience of Gods Order, And," He said: "Disobedience will not enter into the man, but will come out of the man, from his heart; and therefore will he be defiled when he shall eat forbidden food."

The End.
Not Yet Verified.

Source:
Gospel of Barnabas.