Here is the problem...I am your typical explorer and wandered upon High Gate Ruins, so I ventured in and completed the ruins. Later down the road I stumble upon the Meridia's beacon quest which takes me back to High Gate Ruins. I ventured back inside to where I slaughtered Vokoun only to find that both of the steel gated doors are shut and Meridia's beacon is located behind those doors. How exactly does one get back inside the sealed off room? Thanks for your help guys.

I think I had the same issue, there's actually another door which you should use to get in. The barred one is from where you get out when the quest is complete.

If you're standing in front of the altar, the door is located to your right, down the shrine.