Penalty of converting to Christianity

[Hassan Al Zahrani]

This is a thoughtful question, and it's one that Muslims themselves have debated and discussed for centuries.
The verses you cited are indeed among the strongest Qur'anic statements about freedom of belief:

• Qur'an 2:256: "There is no compulsion in religion."
  
• Qur'an 16:82: If people turn away, the Prophet's duty is only to convey the message clearly.
  
• Qur'an 42:48: "We have not sent you as a guardian over them; your duty is only to convey."
  
• Qur'an 88:21–22: "So remind, for you are only a reminder. You are not one to compel them."
  

Taken together, these verses clearly establish that faith itself cannot be forced.
Where does the idea of executing apostates come from?
This is the crucial distinction:
The Qur'an itself never explicitly prescribes a worldly punishment for simply leaving Islam.
The Qur'an frequently mentions people who believe, then disbelieve, and warns them of God's judgment in the Hereafter. For example:

• 2:217
  
• 3:86–91
  
• 4:137 (describes people who believe, disbelieve, believe again, then disbelieve again)
  

Notice something interesting about 4:137: if apostasy alone always required immediate execution, it would be difficult to explain how people could repeatedly enter and leave the faith. The passage speaks of divine judgment rather than a legal penalty.
Why then do many classical scholars say apostasy is punishable by death?
Their position is based primarily on Hadith (reports about the Prophet's words and actions), especially the well-known narration:

"Whoever changes his religion, kill him."

(Classically recorded in Sahih al-Bukhari.)
However, scholars have differed over how this Hadith should be understood.
The traditional interpretation
For many classical jurists, this Hadith established a legal rule that an adult, sane Muslim who knowingly abandoned Islam after due process could be executed.
But they did not usually view this as applying instantly or privately. They imposed numerous legal conditions, including:

• establishing that the apostasy was deliberate,
  
• giving opportunities to reconsider,
  
• requiring judicial proceedings,
  
• prohibiting vigilantism.
  

The alternative interpretation
Many contemporary Muslim scholars argue that the Hadith must be understood in its historical context.
They point out that during the Prophet's lifetime and immediately afterward, "apostasy" often meant more than a private change of belief. It frequently involved:

• joining enemy forces,
  
• committing treason,
  
• inciting armed rebellion,
  
• breaking political treaties with the Muslim community.
  

Under this reading, the death penalty addressed treason during wartime, not mere freedom of conscience.
These scholars note that:

• the Qur'an never orders execution for simply abandoning faith,
  
• the Prophet encountered hypocrites and people who abandoned belief without ordering their execution in every case,
  
• the Qur'an consistently emphasizes that ultimate judgment belongs to God.
  

How do Muslims today view this?
There is no single unanimous view.
Broadly speaking:

• Traditional scholars maintain that classical Islamic law prescribes capital punishment for legally established apostasy, while emphasizing strict judicial safeguards.
  
• Reformist and many contemporary scholars argue that only apostasy accompanied by treason or violent rebellion is punishable, while peaceful conversion to another religion is protected by the Qur'anic principle of "no compulsion in religion."
  

Your observation
Your observation is one of the main arguments made by scholars who reject a death penalty for mere conversion away from Islam. They ask essentially the same question you did:

If the Prophet himself was instructed only to convey the message and not compel belief, where does the Qur'an authorize others to execute someone merely for changing beliefs?

Traditional scholars answer that the authority comes from the Prophet's authenticated Sunnah (Hadith), which they regard as a binding source of Islamic law alongside the Qur'an.
Those who disagree respond that any Hadith must be interpreted consistently with the Qur'an's repeated affirmation of freedom of belief and its silence regarding any earthly punishment for apostasy alone.
So the disagreement is not primarily about the Qur'anic verses you cited—they are accepted by all Muslims—but about how to reconcile those verses with certain Hadith and with the historical circumstances in which they were applied.