This achievement requires you to have a total of 10 divine items CURRENTLY equipped at once, so 8 divine graces and 2 divine relics.
Under the Book of Rea upgrades max out the gem proficiency upgrade to where you’re 100% more likely to find them.
The best levels to go for this would be either 1-3 or 2-2 due to the size of the levels. I personally got this on my 3rd attempt on 2-2 while others had better luck on 1-3, so pick whichever.
Run through the level exploring each floor to the max and opening all gem chests you come across. Make sure you kill all ferocious enemies that you see as they have a chance to drop divine items as well. Also,
be on the look out for “secrets” (the red markings on the floor) as they have a chance to drop divine graces and relics.
On floors 3-4 check out what the vendor is selling and purchase any divine graces you’re missing.
This achievement does require some luck, so keep trying and good luck