People in this world, as per God’s scheme of tests and trials, have been given different resources and different level of knowledge or different opportunities/environment to attain such knowledge.There are different ways that one can opt to serve his religion depending upon his specific situation. Some can serve through the recources they have been provided with, some through the knowledge etc. And a common Muslim is under no religious obligation to opt preaching to the rest of the world. The only responsibity they have is within their immediate circle. Please refer to the following to read more:
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But still if one chooses to preach religion or the right understanding of religion to his community memebers who are not immediate, the best approach would be to have enough knowledge of the matter so as to communicate it clearly and in case of questions, refer it to the scholars.