"7empest" seems to be discussing specific events and/or people, but it's never clear what those are. Because there was a 13-year gap between Fear Inoculum and Tool's previous album, 10,000 Days, there's a broad range of potential world events that could be the target. Whatever the particular identity may be, the song is about a deceptive force creating false serenity to obscure the coming tempest.
A tempest is a violent, windy storm. The term also calls to mind Shakespeare's play The Tempest, thought to have been written around 1610. It's about a sorcerer named Prospero who was shipwrecked with his daughter on a deserted island. Twelve years later, he uses his magic to ground another ship and hatch a plot to get his daughter married and himself back into a position of status. The play is never referenced specifically in "7empest," but Prospero uses dark magic and deception throughout the play, and deception appears to be part of the song's theme.
The repeated mantra, "a tempest must be just that," is saying that this deceptive force, whatever it is, cannot be anything but destructive because destruction is its very nature.
Why the 7 in the song title? That number is a theme on the album; many of the songs are in polyrhythms.
"7empest" is the penultimate song on Fear Inoculum. With a 15:45 run time, it's the longest track on the album.
The song features a chorus riff that Adam Jones had carried around for over two decades. Justin Chancellor told Visions magazine he thinks the Tool guitarist had it filed away since before 1995 when the bassist joined the band. Chancellor added that the riff almost worked on their previous album.
"We tried to use that riff on 10,000 Days but it was only good, not great, so we didn't use it," he said. "In the end, our way of writing music is a long process of experimentation. We enjoy the luxury of taking this very seriously and giving it the time that it needs."
Jones wrote part of the song in a super-complex 21/16 time.