I am simply explaining what the Church believes the gates of hell are. Since you are not Catholic, you are likely to disagree with Catholicism on many more subjects than this one. The icon is, of course, Orthodox and the composition and the meaning of it comes from the Early Church.
Yes, I understand your idea. But that picture is not all that early. It's from the medievil era. I was born and raised a Catholic, attended Catholic schools up to the 12 grade, and in my last two years of high school was being groomed for the priesthood by a priest I thought highly of. I evidently didn't choose that career and with the encouragement of that priest studied religious history and the Scriptures. You would probably think it sad that I read myself right out of the Catholic church. That happened when I was 38 years old. I've actually have more faith in the workings of God and His Christ than I had during my membership in the Catholic denomination of Christianity, thanks to that priest. And yes, I do disagree with the RCC on a few topics; important topics wherein I think they have left what God said in their dust of their building up their organization, the papacy. Scripture teachings were soundly changed very early in the church, and eventually became dogmas one had to believe to be saved...that is what makes me sad for Catholicism.