His Brilliant Zeal Ring was previously a ring that only has a passive ability that protects him from any foreign energy invading his body.
It was a great tool to protect himself against any type of energy that his Mana Shield or Aura Protection could not stop.
As a matter of fact, it had previously contained the energy called Aether which was the energy used by the Xonid Creature. He had almost died at that time.
If he didn't have this ring, he would've succumbed to this unknown and deadly energy that could corrupt almost anything.
This is the reason why Vincent found this ring very important to him. Furthermore, for some reason even after buying another Brilliant Zeal Ring, he was unable to push them to a higher rank than the one that he currently has.
The other Brilliant Zeal Ring he tried to ascend had only reached Epic Rank and a couple of Pseudo-Legendary Ranks.