We are however called to evangelise, so his questions are important and valid. While yes, Protestants can find the truth on their own, clearly we aren't just meant to sit back and let things fall as they may, for we were called to evangelise and convert the world.
I'm not disagreeing with this.
I am saying that given the situation today, while it might seem impossible to explain the necessity of belonging to the Church and what happened to it, it really is entirely possible even if one cannot explain it well or explain it fully - that ultimately it is dependent upon the person listening, if they sincerely want to know the truth of the matter, they will find the truth of the matter. If they really want to know, then your explaining it to them will prompt them to do their own seeking and searching, in that way there is much they will find out to put them on the right road.
Conversely, no amount of explaining will suffice to those who really do not want to know.