The harvest (refining) process is ongoing throughout the book from the churches, through the seals and trumpets, but seems to become more intense starting in chapter 12 with the woman and child, the dragon, the leopard beast, the lamb beast, and climaxing with the sickle.
Sometimes it is difficult to understand God's methods. God's people from the Philadelphia type of church are "kept from the time of trial." (3:10). Whereas God's people from the Smyrna type of church are told, "Do not be afraid of what you are about to suffer...you will suffer persecution for ten days." (2:10).*
No doubt both groups are used mightily by God. Those called to heaven are likely to be busy building God's city, whereas those on earth are likely to be busy leading others to God -- by example and by word when asked (as in 1 Peter 3:15).
*Ten days: Is this a literal 10 days? Does it mean 10,000 years? Does it mean 10 years? Or something else? During the transition to a new era, the persecution is likely to last at least a literal 3.5 years. 3.5 years are mentioned 3 times in chapter 11 (11:2, 3 & 11); twice in chapter 12 (12:6 & 14) and once in chapter 13 (verse 5). It's possible all three references in chapter 11 are the same period. Both in chapter 12 maybe the same period, but they seem to come after those in chapter 11. The period in chapter 13 may overlap, at least a part, of the period in chapter 12. Five months is mentioned twice in chapter 9 (verses 5 & 10), both of these seem to indicate the same period of time.
The Great Dragon Leads The World Astray
The Beast Out Of The Sea (Leopard Beast)
The Beast Out Of The Earth (Lamb Beast)