What is Jesus promising when he says he’ll keep the faithful Philadelphian Christians from the “hour of testing” (3:10)? Is this talking about a pre-tribulation rapture?
This is one of the few places in Revelation where some interpreters see a reference to a rapture of Christians before a seven-year great tribulation. Three main lines of evidence are used to support this:
1) Jesus’ language about an “hour of testing that is going to come on the whole world to test those who live on the earth” is widely agreed to be a reference to the terrifying judgment of God at the end of history. 
2) The specific Greek wording of being “kept from” that “hour” of testing seems to imply total, physical separation from that time period, and not merely spiritual protection through it. 
3) The letters to the seven churches have implications for all Christians everywhere (as I belabored in my previous post), so something of this promise should be relevant to all those “with ears to hear” in any generation. 
On all of these details, I am actually inclined to agree with pre-trib interpreters. But, there’s one interesting little fact that most supporters of a pre-tribulation rapture often miss that really hurts their position, and it’s that the “hour” is not the whole tribulation!
When Jesus refers to “the hour of testing,” he’s not referring to a seven-year period of tribulation, but to a very limited time at the tail end of the tribulation!
The tribulation is consistently referred to throughout Revelation with the time-reference “1,260 days,” or three and a half years (Rev 11:3; 12:6, 14; derived from the “half-week” prophecy of Daniel 9:27). Nowhere is it described as an “hour.” In fact, Allen Kerkeslager points out that instances of an “hour” of time in Revelation always refer to the very final day, at the end of the tribulation, when Christ returns and the evil empire of “Babylon” is finally overthrown (Rev 11:11-13; 14:7, 15; 18:10, 17, 19). 
We also see this kind of time reference in the Gospels, where Jesus consistently refers to the time of his actual Second Coming as “that day or that hour” (Matt 24:44, 50; 25:13; Luke 12:39-40, 46; John 5:25).  This will be the time when God’s full wrath is vented on unbelievers on the earth, when he overthrows “Babylon” in “a single hour.”
Believers will be delivered from that horrible day by the post-tribulation rapture, which will happen concurrently with Christ’s descent from heaven at the Second Coming (see Mark 13:24-27; 1 Thes 4:16-17; 1 Cor 15:52).
Since Christians living in the first century believed that the events leading up to Christ’s return could begin taking place any day, this promise that they would not experience the day of final wrath on the earth was applicable to them just as it is to us should we happen to be alive at the end. The Philadelphian Christians just happened to experience this protection through their physical deaths, which technically is still a form of physical separation from an earthly trial!
These Christians — and us, as well — would still have to be faithful through all other trials (including the possibility of imprisonment or martyrdom for their faith, as well as the attacks of the coming Beast and his empire). But these will pale in comparison to the outpouring of God’s full and final wrath on non-believers on the last day of history. That hour of trial we are exempt from, by the grace of God through our faith in Christ.
All of this information lines up with the fact that elsewhere in Scripture and in Revelation believers are told to endure to the very end, when Christ will appear to the whole world (Matt 24:13; Mark 13:13; 2 Thes 2:1-10; 1 Pet 4:12-13; Rev 7:14; 13:10).
To sum up: The “hour of testing” is not referring to the whole time of tribulation, but only to the events connected with the very final day of history and the Second Coming, when Christ descends from heaven and God pours out his final wrath on “Babylon” and those who worship the Beast. When Christ promises believers in Rev 3:10 that he will “keep” them from this hour of trial, it is indeed via the rapture, but I’m convinced this will be a post-tribulation rapture!
 See Grant R. Osborne, Revelation, BECNT (Baker, 2002), 193. He calls this the consensus view, and summarizes the usual two pieces of support: the global scope of the trial and the fact that “those who dwell on the earth” is a stock phrase throughout the book for unbelievers who follow the Beast. Osborne takes a post-tribulational view, though.
 See Buist M. Fanning, Revelation, ZECNT (Zondervan, 2020), 177 for some pretty convincing arguments why we shouldn’t see Rev 3:10 as merely referring to spiritual preservation through the tribulation, and why supposed parallels with John 17:15 won’t work.
 Though see Sam Storms’ blog post, “Kept From the Hour of Trial (Revelation 3:10-11),” for an example of the view that Rev 3:10 is in fact a promise only for the first-century Philadelphian church. This used to be my own approach.
 Allen R. Kerkeslager, “The Day of the Lord, the ‘Hour’ in the Book of Revelation, and Rev 3:10,” unpublished paper delivered at the annual 1991 Annual Meeting of the Society of Biblical Literature; cited in G. K. Beale, Revelation, NIGTC (Eerdmans, 1999), 292.
 John Murray, “The Interadventual Period and the Advent: Matthew 24-25,” reprinted in his Collected Writings, Vol. 2 (Banner of Truth Trust, 1996), 394-95; cited in Jonathan Menn, Biblical Eschatology: Second Edition (Resource Publications, 2018), 142-43.