***Playing devil’s advocate, the sola scriptura answer would be “I KNOW — that’s God’s promise to me. Why don’t you believe and have the same belief? Christ died for us, so why doubt Him???”***
There are two immediate considerations. The first is that how does one know that one interprets Scripture correctly? The second is that how does one know that one’s belief is the same belief that Jesus gave to the Apostles.
In neither case, outside of the Church, does one have any assurance that their beliefs are correct or anywhere near correct. The Reverend Jim Jones, pre Kool Aid dispensing, no doubt absolutely believed that his faith was the correct one. The JWs believe. The LDS believe. And so on.
Jesus preached one church and one belief. The plethora of beliefs give lie to the odd notion that the Protestant Reformation, the Restoration and the subsequent buddings bring us correct beliefs.