Seven is the number of completion, so the “seven spirits” are one. There are seven churches because that is the complete set of churches. In binary, seven is 111, so a trinity of ones is complete, or one.
The Ein Sof manifests Himself in His creation as the Trinity, Father, Son, Holy Spirit as a consequence of how He created the Universe:
And He created His universe with three books (Sepharim), with text (Sepher) with number (Sephar) and with communication (Sippur).
Kaplan, Aryeh (2004-03-15). Sefer Yetzirah: The Book of Creation in Theory and Practice (Kindle Locations 445-449). Red Wheel Weiser. Kindle Edition.
The Universe is an accounting system. That is how we, as sinners, can be saved by believing in Jesus Christ so that His Righteousness is credited to our account.
There is an interesting passage in 2Thess2, where Paul refers to 'the restrainer' being taken out of the way, so the full measure of the lawlessness can be revealed ...