You may want to consider the following scriptures, facts, and reasonings with your friend, for this is just one of many identifying marks of true religion:
A most important way in which Christ's true disciples can be identified is by the love they have among themselves. Jesus said: "By this all will know that you are my disciples, if you have love among yourselves." (John 13:35) Do the religious organizations with which you are acquainted have this love? What do they do, for example, when the countries in which they live go to war against one another?
You know what usually happens. At the command of worldly men the members of the various religious organizations go out on the battlefield and slaughter their fellow believers of another country. Thus Catholic kills Catholic, Protestant kills Protestant, Mormon kills Mormon, and Muslim kills Muslim. Do you think such a course is according to God's Word and really shows the spirit of God?-1 John 3:10-12.
How do true Christians measure up in this matter of showing love to one another? They do not follow the course of worldly religions. They do not slaughter fellow believers on battlefields. They have not been guilty of living a lie by saying, "I love God," while hating their brother of another nationality, tribe or race. (1 John 4:20, 21) But they also show love in other ways. How? By the way they deal with their neighbors and by their loving efforts to help others to learn about God.-Galatians 6:10.
Who are these true Christians?