A Gentle Welcome: by CS Lewis

There is one body and one Spirit-- just as you were called to one hope when you were called--  one Lord, one faith, one baptism;   one God and Father of all, who is over all and through all and in all.  But to each one of us grace has been given as Christ apportioned it.  This is why it says: "When he ascended on high, he led captives in his train and gave gifts to men." Ephesians 4:4-8

I hope no reader will suppose that 'mere' Christianity is here put forward as an alternative to the creeds of the existing communions. .... It is more like a hall out of which doors open into several rooms. If I can bring anyone into that hall I shall have done what I attempted. But it is in the rooms, not in the hall, that there are fires and chairs and meals. The hall is a place to wait in, a place from which to try the various doors, not a place to live in. For that purpose the worst of the rooms (whichever that may be) is, I think, preferable. It is true that some people may find they have to wait in the hall for a considerable time, while others feel certain almost at once which door they must knock at. I do not know why there is this difference, but I am sure God keeps no one waiting unless He sees that it is good for him to wait. When you do get into your room you will find that the long wait has done you some kind of good which you would not have had otherwise. But you must regard it as waiting, not as camping. You must keep on praying for light: and, of course, even in the hall, you must begin trying to obey the rules which are common to the whole house. And above all you must be asking which door is the true one; not which pleases you best by its paint and panelling. In plain language, the question should never be: 'Do I like that kind of service?' but 'Are these doctrines true: Is holiness here? Does my conscience move me towards this? Is my reluctance to knock at this door due to my pride, or my mere taste, or my personal dislike of this particular door-keeper?'

When you have reached your own room, be kind to those who have chosen different doors and to those who are still in the hall. If they are wrong they need your prayers all the more; and if they are your enemies, then you are under orders to pray for them. That is one of the rules common to the whole house.