Why was drinking alcohol not prohibited in earlier religions? As people generally say: If it is so disastrous for the faculty of reasoning then it should have been disallowed for the earlier religions also?
It is not correct to say that intoxicants were not prohibited in previous revelations. Intoxicants are a part of the natural prohibitions due to their potential affect on the human faculty of reasoning.
Leviticus 10: 8 – 11 read as follows:
The LORD then spoke to Aaron, saying: “Do not drink wine or strong drink, neither you nor your sons with you, when you come into the tent of meeting, so that you will not die – it is a perpetual statute throughout your generations – and so as to make a distinction between the holy and the profane, and between the unclean and the clean, and so as to teach the sons of Israel all the statutes which the LORD has spoken to them through Moses.”
Note the similarity between this directive of Leviticus and that of Al-Nisaa 4: 43.
In Judges 13: 4, intoxicants (strong drink) have clearly been grouped with unclean things:
[The angel said:] Now therefore, be careful not to drink wine or strong drink, nor eat any unclean thing
Proverbs 20: 1 says:
Wine is a mocker, strong drink is raging, And whosoever is deceived thereby is not wise.
Matthew Henry, in his commentary on the whole Bible writes:
The mischief of drunkenness: Wine is a mocker; strong drink is raging. It is so to the sinner himself; it mocks him, makes a fool of him, promises him that satisfaction which it can never give him. It smiles upon him at first, but at the last it bites. In reflection upon it, it rages in his conscience. It is raging in the body, puts the humours into a ferment. When the wine is in the wit is out, and then the man, according as his natural temper is, either mocks like a fool or rages like a madman. Drunkenness, which pretends to be a sociable thing, renders men unfit for society, for it makes them abusive with their tongues and outrageous in their passions…
Proverbs 31: 4 – 5 reads:
It is not for kings, O Lemuel, It is not for kings to drink wine, Or for rulers to desire strong drink. For they will drink and forget what is decreed, And pervert the rights of all the afflicted.
Luke 1: 15, introducing John the Baptist notes:
“For he will be great in the sight of the Lord; and he will drink no wine or liquor, and he will be filled with the Holy Spirit while yet in his mother’s womb.”
Galatians 5: 19 – 21 read as:
Now the deeds of the flesh are evident, which are: immorality, impurity, sensuality, idolatry, sorcery, enmities, strife, jealousy, outbursts of anger, disputes, dissensions, factions, envying, drunkenness, carousing, and things like these, of which I forewarn you, just as I have forewarned you, that those who practice such things will not inherit the kingdom of God.
We hope this helps.