That scripture, Revelation 3:10, was written to one of seven churches: Philadelphia. Additionally, it was written to that church, referring to things that were presently occurring, and soon to occur in that church. Jesus told John in Revelation 1:19 that he was to "write the things which thou hast seen, and the things which are, and the things which shall be hereafter."
We must first consider that this speaks about the way things were in Philadelphia. If there are principles that may be broadly applied, we may do so. To say that all future believers will be kept from testing is not true or accurate. To also imply that any protection that will accrue to believers must involve their removal by rapture from the Earth is not true or accurate either. God is able to protect us, as he protected Noah in the Ark and the Israelites in Goshen.
Following this, seven existing churches are addressed. I take this to be things present are being talked about. Then, in Revelation 4:1, after the seven churches discourse is finished, John is told, "Come up hither, and I will show thee things which must be hereafter."
One thing is clear: Revelation must have some "things which are" in the book, because that is what Jesus told John in 1:19. Those things after 4:1 are called "things which must be hereafter".