All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger. {C}
It is necessary to differentiate between two categories of people:
The one who commits sins and insists on committing them, while he acknowledges their prohibition and testifies that the Sharee'ah prohibited them: this person is a Muslim for whom we hope the same thing as we hope for any other Muslim, and he is treated in the like manner as the disobedient Muslim. Therefore, he should be called to Allah and frightened of His punishment if he insists on his disobedience. If he dies on this state, he is under the Will of Allah Almighty; He may punish him if He so wishes, or forgive him if He so wishes.
The other category is one who denies what is known with absolute evidence in the religion, like the one who denies that the prayer is an obligation, or that alcohol is forbidden, and so forth: such a person is a non-Muslim and goes out of the fold of Islam. However, if such a person is ignorant of the ruling because he is a new Muslim, or because the texts of the Sharee'ah did not reach him because he lives very far from the land of Islam; such a person is not ruled to be a non-Muslim until the evidence is established against him and the ruling of the Sharee'ah is clarified to him.
Each of the two groups of people should be called in a manner that suites their condition. The first group should be admonished, reminded, and frightened about the Hereafter and the punishment that is prepared for the disobedient people. They should be reminded of the evil consequence of sins on ones faith as well as his worldly life.
The second group should be told that what they do is contrary to Islam and the message with which Allah sent His Prophet and that if he dies upon this belief, then he will be eternally in Hellfire -we seek refuge in Allah from this.
The one calling to Allah, especially in such countries, should be kind and soft (when calling others to Allah) as much as possible, and should follow the most effective ways in reminding people, and the most influential method in clarifying the matter according to the situation.
For more benefit, please refer to Fataawa 6512, 10157, and 14264.
Allah knows best.