The style of the revelation of the Quran was gradual, over a period of 23 years. A command would initially be revealed in much general terms. This was done to ease Muslims into the new Divine regulations. When the initial command is absorbed by Muslims, God followed it with more details about it, such as how to implement it properly. Many scholars thought that subsequent commands were abrogation of the initial command! But that is incorrect, since abrogation means cancellation, and the initial command always remained in force.
A good example of that is the prohibition of drinking alcoholic beverages. The first command God sent down on this issue was,
“And from the fruits of the palm trees and grapevines you take for yourselves intoxicant and good provision. Verily, in that is a sign for a folk who reason.” (16:67)
Here is a very subtle indication that intoxicants are not a good thing. God leaves the word without an adjective to describe it, but He follows the word “provision” with the adjective “good.” Those who got the hint, Umar ibn Al-Khattaab (RA) was one, understood that God is not pleased with alcoholic beverages.
A subsequent command was then revealed,
“They ask you about intoxicants and easy gain (gambling). Say: In them is major sin and benefits for people. But their sin is bigger than their benefit.” (2:219)
So, those who did not notice before are now left with no doubt that alcohol is bad. Notice that this verse does not abrogate 16:67, because not describing something as being good is tantamount to describing it as more bad than good!
Then, a third command was revealed,
“O you who have believed, do not approach prayer while you are intoxicated until you know what you are saying, ” (4:43)
Now the matter is getting serious; intoxication prevents a Muslim from even approaching a prayer! Still, many people thought that it was OK to drink outside prayer times! They still didn’t get the hint. You see why God is walking them those baby steps? It is very hard for a society used to drinking alcohol to quit that habit. They need training. That is what God was doing, out of His Grace, by the gradual revelation of these commands. Notice also that this verse does not abrogate either of the aforementioned verses, because not praying while drunk does not mean drinking is allowed.
Finally, the prohibition was revealed in no uncertain terms,
“O you who have believed! Verily, intoxicants, easy gain (gambling), [sacrificing on] stone alters [to other than God], and divining arrows are but defilement from the work of Satan, so avoid it that perhaps you may prosper.
Verily, Satan only wants to drop between you enmity and acrimony through intoxicants and easy gain (gambling) and to shun you from the remembrance of God and from prayer. So, are you ceasing?” (5:90-91)
It is of particular interest to notice that Chapter 5 was one of the very last chapters of the Quran to be revealed. That means that the prohibition of alcohol took the entire period of revelation between Chapter 16 and Chapter 5, almost a decade!
That is just one example of why the Quran may not start off a command with the clear statement outright.