I read most of the story six months ago. Give me a break.
Spoiler for blessings:
The speed only lasts for an instant - from Kurono's perspective, the time slows down, and by concentrating he can use this opportunity to avoid otherwise fatal attacks. The armor lasts... a bit longer? The strength... even longer? They're good mostly for PvP battles, not for huge AoE-scale attacks. Kurono is powerful, but not OP. Although many in the story would say otherwise.
It also puts a strain on Kurono if he uses them too much, or in succession.
IIRC the blessings also allow Kurono to emulate the elements with his Black Magic. The first one is fire, the second one is steel, the third one is lightning, and the fourth one is... love? At least according to chapter 471.
