Call to the way of your Lord with wisdom and fair admonition, and argue with them in the kindest way. Your Lord knows best who is misguided from His way. And He knows best who are guided. (Surat an-Nahl; 125)
Islam is acceptable to Allah only when a person lives by it sincerely, willingly and happily, and only when the person himself consents to it. Allah has revealed this quality of religion in many verses of the Qur'an. For example, a person who prays must do it willingly and lovingly for Allah. Or if someone gives gifts from his possessions, he must do it willingly and lovingly, if his act of worship is to be approved in Allah's sight.
Someone becomes a Muslim when he is able to acknowledge Allah through his intellect and in his heart. Moreover, he must be conscious of the purpose of his religious duties. And he must be aware of why he performed these acts of service. This comes from his attachment to the Muslim religion and his belief in Allah's existence. For this reason, he performs the requirements of religion willingly and lovingly.
Therefore, Islam is a religion whose true practice depends on the voluntary choice of the individual.
Hence, there is no compulsion to accept Islam. Allah does not expect Muslims to pressure those who do not incline towards Islam, since religion accepted under oppression is not acceptable in His sight. Experiencing religion without sincerity and only because of pressure from others will have no validity before Allah. Therefore it will make no difference for anyone to practice religion with this kind of morality.
Communicating the religion of Islam to others should be an invitation made with gracious words, as a summons to a relationship with Allah. Here is a verse which says that there is no coercion in religion:
There is no compulsion where the religion is concerned. Right guidance has become clearly distinct from error. Anyone who rejects false gods and believes in Allah has grasped the Firmest Handhold, which will never give way. Allah is All-Hearing, All-Knowing. (Surat al-Baqara; 256)
In compliance with Qur'anic instruction, when explaining the religion of Allah, Muslims employ the best style that will kindle love in the hearts of people towards Islam. They must be kind and patient. When people can love and respect Muslims, they will be receptive to the system of beliefs that gave them moral excellence. Therefore, the right word will be important to soften their hearts to Islam.