You will come to a people of the Scripture. When you reach them, invite them to testify that none is worthy of worship except Allah and that Muhammad is the Messenger of Allah

Explanation

When the Prophet (may Allah's peace and blessings be upon him) sent Mu‘ādh ibn Jabal (may Allah be pleased with him) to Yemen to call its people to Allah and teach them, he clarified to him that he would meet Christian people and that he should first call them to what is more important and then to what is less important, and so on. He should first call them to reform their creed by testifying that none is worthy of worship except Allah and that Muhammad is the Messenger of Allah. This is because they enter Islam with this testimony. If they complied with that, he should then enjoin them to establish the prayer, for it is the most important obligation after the testimony of Tawhīd (monotheistic belief). If they established the prayer, he should then order the rich amongst them to pay Zakah on their property to the poor amongst them. Thereafter, the Prophet (may Allah's peace and blessings be upon him) warned him not to take their best property; instead, it is required to adopt a moderate approach in this regard. Then, he (may Allah's peace and blessings be upon him) instructed him to avoid oppression, lest an oppressed person might supplicate to Allah against him, as his supplication is readily answered.

Benefits

• The testimony that none is worthy of worship except Allah means that we should devote worship to Allah Almighty alone and shun the worship of all other things.
• The testimony that Muhammad is the Messenger of Allah means to have faith in him and what he came with, to believe in him, and to believe that he is the last Messenger sent by Allah to all humankind.
• Speaking to a knowledgeable person or someone with certain misconceptions differs from speaking to an ignorant one. Hence, the Prophet (may Allah's peace and blessings be upon him) alerted Mu‘ādh with his words: "You will come to a people of the Scripture."
• It is important for a Muslim to have proper knowledge of his religion to get rid of the misconceptions of those who raise them.
• It demonstrates the invalidity of the religion of the Jews and the Christians after the mission of Prophet Muhammad (may Allah's peace and blessings be upon him) and that they are not among the people who will attain salvation on the Day of Judgment unless they enter the religion of Islam and believe in the Prophet (may Allah's peace and blessings be upon him).