User blog comment:B214/Shin DxD 1 discussion/@comment-95.210.189.106-20180815144003/@comment-28884330-20180817010556

Saji’s Sacred Gears can not evolve into Longinus simply because their power source is not strong enough to kill Gods. A Sacred Gear cannot make power out of nowhere, and since Saji’s power source is lower than Satan-class, then around that level is the most it can possibly output.