What is the ruling on doubting the Islamic religion and changing one's religion?

Islam is the true religion with which Allah concluded the religions. The proofs of its being the true religion are numerous, and doubting this truth constitutes disbelief in Allah the Almighty, for He says: "The believers are only those who have believed in Allah and His Messenger and then doubt not but strive with their properties and their lives in the cause of Allah. Those are the truthful." Allah has abrogated every other religion with Islam, and whoever seeks a religion other than Islam, it will never be accepted from him, and in the Hereafter, he will be among the losers, as Allah the Almighty says: "And whoever seeks a religion other than Islam, it will never be accepted from him, and in the Hereafter, he will be among the losers." Christianity is a corrupted religion containing many falsehoods, and abandoning Islam and entering Christianity is considered apostasy from Islam, leading to loss in this world and the Hereafter. Allah says: "And whoever among you reverts from his religion [to disbelief] and dies while he is a disbeliever - then those have become worthless [all] their deeds in [this] world and the Hereafter, and those are the companions of the Fire; they will abide therein eternally." Allah is indeed self-sufficient, having no need for our faith or our acts of obedience. The obedience of the obedient does not benefit Him, and the disobedience of the disobedient does not harm Him.