This Magic allows the user to surrounds a their witch soul, making their wavelength completely disappear. Their soul is then camouflaged as a normal, human soul as a result. The spell was created to counter the Soul Perception ability. The spell is powerful enough to evade detection from even extremely skilled Meisters as well as Death Gods.
Under Soul Protect, however, an individual is unable to use any of their Magic while under the spell.
Soul Protect has additional advantages as well; Eruka Frog explains to members of the DWMA that, with a sufficient number of witches, a simultaneous use of Soul Protect could prevent the Kishin from using his Madness Wavelength to infinitely regenerate Clowns, a practice that was important in the DWMA's victory against Asura and the Clown Army on The Moon.
Although Soul Protect is difficult to pierce, there's only two known ways. It was speculated by Sid Barrett that a technique to piercing Soul Protect was possible, but still required one to become a Kishin for the possibility to be there. And only select individuals with Super Soul Perception have the ability to see through a Soul Protect.