The key to Revelation is the Old Testament. Think of it as a key code for unlocking the prophesy of Revelation. All of the New Testament is the Old Testament revealed, and fulfilled. So, the reader must find the prophetic judgment language as it was originally used in the Old Testament.
Then, the time texts are key. Revelation was the prophesy of the battle of Christ against His enemies - those who pierced Him and who were persecuting His newly born church. As an historian will write the record of a war from different battle fronts, so Revelation works through the battle from the view of the throne scene in Chaps. 4 - 11, and then turns to retrace the battle front from the church and the beasts in Chap. 12.
Chap. 12 outlines the birth of Christ and the church in the first part of the first century A.D. - events that had already happened before the book was written, and before the prophesy was shown to John n- and then moves forward to the battle. Then Chaps. 13 - 19 deal with the battle as was shown in chaps. 4 -11 but from the point of view of church.
So, the angels with the seven trumpets parallel the angels with the seven bowls. The first of each were cast upon the earth; the second upon the sea; the third upon the rivers and springs; the fourth upon the sun, moon, and stars; the fifth released the locust army of the sea beast; the sixth sounded the call to the full battle itself; and the seventh sounded the completion of the battle.
Each set was tied to the plagues of Egypt which God had told Israel He would pour out upon them if they broke His covenant and did not keep His laws.
“Moreover he will bring upon thee all the diseases of Egypt, which thou wast afraid of; and they shall cleave unto thee. 61 Also every sickness, and every plague, which is not written in the book of this law, them will the Lord bring upon thee, until thou be destroyed.” (KJV)
Everyone struggles with Revelation because they do not pay attention to the time texts, and they do not find the code from the Old Testament. Revelation parallels Ezek. chap. 5, which was judgment pronounced upon Israel.