Correction, we know because Christ told us. Ignore His word at your peril. Catholicism IS the guardian of the Truth of Christ. Or perhaps the 31,000 Protestant denominations, all of whom disagree on many things, have a better handle on it? I think not. But hey, I'm just going by what Christ said. Do you presume to say you know better than Christ?
Ignore His Word at your peril. Catholocism condemns all who do not believe that there is a co-mediatrix (Mary) despite clear text telling us this is not so? Do you say you know better than God? Or perhaps the 2XX + popes, many of whom have disagreed on many things, have a better handle on it. But hey, I'm just going by God's inspired word. Do you presume to say you know better than God?
What then is the truth of Christ? His Word or a tradition of the RCC? We all must decide this for ourselves I suppose.