How can one get rid of deviation and doubt in creed, especially when hearing arguments from other schools of thought or from people of other religions, and how can one remain steadfast in the creed of Ahlus-Sunnah wal-Jama'ah?

The path to Paradise is one and straight, and it is what the Messenger of Allah, peace and blessings be upon him, guided us to, for Allah Almighty says: "And indeed, this is My straight path, so follow it, and do not follow the [other] ways, for they will diverge you from His way." One must adhere to the truth and avoid the people of desires and their doubts, and learn the sciences of Sharia to strengthen faith, and read books of creed and the Prophet's biography. Jews and Christians are disbelievers and their destiny is Hellfire, for Allah Almighty says: "Indeed, those who disbelieved among the People of the Scripture and the polytheists will be in the fire of Hell, abiding eternally therein. Those are the worst of creatures," and for the saying of the Prophet, peace and blessings be upon him: "By Him in whose hand is my soul, no Jew or Christian from this nation hears of me and then does not believe in me, except that he enters the Fire." The most important reason for steadfastness is to ask Allah for guidance and to frequently say: "O Turner of hearts, keep my heart firm upon Your religion."