See related “Topic Studies & Terms”:
“One Hundred Forty Four Thousand (144,000 of Revelation chapters 7 and 14)”
For a more in-depth study see the related full “Study Series” (available upon request if not hyperlinked):
“Study Series 8 Lesson 1 God’s Festal Calendar (Spring Feasts)”
“Study Series 16 Lesson 2 Rev. Chapters 5 thru 9”
“Study Series 16 Lesson 5 Rev. Chapters 14 thru 16”