You're exactly right because that's what's wrong with Catholic theology.
They take one verse out of context and build on it: the papacy, the perpetual virginity of Mary, the immaculate conception, works based salvation, a priest having the ability to forgive someone else's sin, transubstantiation, apostolic succession, to name a few.
All based on one verse, usually very loosely translated.
That's why *Protestant* theology stands head and shoulders above Catholic theology. Because Scripture interprets Scripture and any Christian worth their salt demands multiple passages of Scripture to defend a belief, not just ONE verse.
There is NO such thing as Protestant theology. 35,000 sects of them have littered the steers with Biblical chaos, the inevitable outcome of a denial of Petrine authority. Protestant “theology” or whatever is whenever any Protestant cracks open the Bible and runs with a scriptural quote from Jim Jones to Billy Graham to Joel Osteen and Rev. Wright making personal fortunes on the way. This is why there are now a slew of scholarly articles trying to explain why Bible Christians are so shallow.