Martin Luther on Standing Against the Pope

"Daily I feel how difficult it is to divest oneself of scruples long entertained. Oh! The pain it has cost me, though with the Scriptures before me, to justify myself to myself, for daring singly to set myself up against the Pope, and hold him as Antichrist! What tribulations have I not suffered! How often have I not addressed to myself in bitterness of the spirit the arguments of the Papists: 'Art thou alone wise? Are all others in error? Can they have been so many years deceived? What if thou deceivest thyself, and draggest along with thee in thy error so many souls to everlasting damnation?' Thus I used to argue within myself until Jesus Christ with His own, His infallible Word, fortified me, and strengthened my soul against such arguments, as a rock raised above the waves laughs their fury to scorn." (Letters, Vol. 2, p. 107.)

From:  Let Luther Speak for Himself.