Why Islam always prohibits the paradise for small things? for example dying the hair colour black without any bad intention, or to make the wife happy. Islam says one will not even smell the paradise because of this. Islam also says plucking the eyebrows for husband is prohibited. why Islam is too strict on even very small things which are not even harmful for health or others, without any bad intentions.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

Islamic rulings are a Legislation from Allaah, the Lord of the heavens and the earth, The All-knower, The All-Wise, Who does not legislate anything except with knowledge and wisdom. Allaah Says (what means): {And the word of your Lord has been fulfilled in truth and in Justice. None can alter His words, and He is the Hearing, the Knowing.} [Quran: 115]

Therefore, Allaah rules and it is not permissible for anyone of His creation to object to His Judgment. Allaah Says (what means): {And Allaah decides; there is no adjuster of His decision. And He is swift in account.} [Quran 13:41]

Hence, it is obligatory upon His slaves to be satisfied with His rulings and submit themselves to them. This is indeed among the requirement of faith, as Allaah Says (what means): {But no, by your Lord, they will not [truly] believe until they make you, [O Muhammad ], judge concerning that over which they dispute among themselves and then find within themselves no discomfort from what you have judged and submit in [full, willing] submission.} [Quran 4:65]

However, it is permissible for a Muslim to seek the wisdom behind a ruling while being satisfied with it and after submitting himself to it and to his Lord, or that he asks a question about it in order to know but not to ask while objecting to the Judgment of Allaah as an act of being ill-mannered towards Allaah.

Moreover, you should know that Allaah has not forbidden anything except that its evils are greater than its benefits, if it has any benefits, as it might be that there are only evils in it and no benefits at all.

Allaah has legislated for us all beneficial matters and He has made forbidden to us any harmful matter. No doubt, Allaah does not prohibit something except that there is harm in it which we may or may not know.

Allaah is the Creator, and so He is more aware of what benefits His Slaves and what harms them; hence He is the Legislator. Allaah Says (what means): {Does He who created not know, while He is the Subtle, the Acquainted?} [Quran 67:14] Allaah also Says (what means): {His is the creation and the command; blessed is Allaah, Lord of the worlds.}[Quran 7:54]

As regards the sins, there are minor and major sins, but the minor sins are great taking into consideration the greatness of Allaah, it is for this reason that some scholars of the Salaf (righteous predecessors) said: “Do not look to the smallness of the sin, but look to the greatness of the One Whom you disobeyed.”

On the other hand, insisting on small sins renders them grave sins; as stated by Ibn ‘Abbas, may Allah be pleased with him: “There is no minor sin while persisting on it, and there is no major sin while seeking Allaah’s Forgiveness for it.” For more benefit, please refer to Fatwa 116246.

Under any estimation, there is no strictness in Sharee’ah in what is proven forbidden by text. The dispraised strictness is to forbid what is lawful, or to worship Allaah with an act that is not legislated as an act of worship and so forth. However, if the Sharee’ah is contrary to the desires of people, then it is not strictness at all because if this door is open and the matter is left to the desires of the people in issuing rulings on things, then the religion will be lost and its features will be effaced. Allaah Says (what means): {But if the Truth [i.e. Allaah] had followed their inclinations, the heavens and the earth and whoever is in them would have been ruined. Rather, We have brought them their message, but they, from their message, are turning away.} [Quran 23:71]

Allaah Knows best.