Meeting Abdirak in the Shattered Sanctum in Baldur's Gate 3 is quite an easy encounter to miss if you're engrossed with trying to find Halsin or assassinate the goblin leaders, but it can give you a powerful boon if you take the time to stop by. This servant of Loviatar, goddess of pain, is hanging out in the Bloodied Shrine, directly east of where Priestess Gut is standing on the platform.
If you're willing to let Abdirak hurt you or any of your companions a bit, you can gain a permanent condition that provides a combat bonus. While there, make sure to rescue Volo the bard next door, or not, I guess, if you're evil. All that said, here's how to get Loviatar's Blessing from Abdirak.
To get the blessing of the goddess of pain, you're going to have to let Abdirak smack you about with a mace, while you pass some skill checks to put on a convincing show that you're having a grand old time. There are three checks overall that you need to pass to gain the blessing, and you can use either Performance or Intimidation. Don't choose the Constitution check option since passing these will result in failure. Abdirak wants you to embrace the pain rather than hold it in, after all.
If you read the On Receiving Her Grace and Screed of the Willing books in the Bloodied Shrine, you can also choose which weapon he hits you with, though this makes no difference to whether you get the blessing or not. If you're wounded to the point where Abdirak's blows would kill you, he'll also ask you to heal up first. Upon successfully taking all hits and passing all three checks, you'll get the Loviatar's Love condition which means when you have 30% hitpoints or less, you gain +2 to Attack Rolls and Wisdom Saving Throws for three turns. This shows up in conditions as Basking in Loviatar's Love when you hit the required HP threshold.
If your run-in with Abdirak has convinced you to flagellate yourself in combat, then you'll want to steal the Ritual Dagger on the side table in the Bloodied Shrine. This weapon has an ability called Blood Sacrifice, which lets you take 1-4 Slashing damage in exchange for a bonus 1d4 to Attack Rolls and Saving Throws. Lastly, this might be a bug, but you lose the Loviatar's Love condition if your character dies and is resurrected, so play safe.