God knew that even in the Muslim Ummah there will be many people who claim to be Muslims (i.e. claim to submit their will to God) but practically will not follow God’s commandments.
GOD REFERS TO SUCH PEOPLE IN THE QURAN AS LIP SERVICE BELIEVERS
“O messenger, do not be saddened by those who increase in disbelief from among those who said: “We believe” with their mouths while their hearts did not believe…” (Qur’an 5:41).
Thus we can conclude that those who claim to be Muslims but do not believe the Quran is fully detailed, complete, and enough for believers and those who divide themselves in to sects are Lip-Service Muslims.