Actually it is quite simple and without flaw – because it is not based on our mind, heart, will or intellect…reasoning or science…it is based on something God has done (Divine Revelation) and given us (Grace) to respond to Him in obedience…it is called:
[LEFT]CATECHISM OF THE CATHOLIC CHURCH
By his Revelation, "the invisible God, from the fullness of his love, addresses men as his friends, and moves among them, in order to invite and receive them into his own company."1 The adequate response to this invitation is faith.
143 By faith, man completely** submits his intellect and his will to God**.2 With his whole being man gives his assent to God the revealer. Sacred Scripture calls** this human response to God**, the author of revelation, “the obedience of faith”.3
150 Faith is first of all a personal adherence of man to God. At the same time, and inseparably, it is** a free assent to the whole truth that God has revealed.** As personal adherence to God and assent to his truth, Christian faith differs from our faith in any human person. It is right and just to entrust oneself wholly to God and to believe absolutely what he says. It would be futile and false to place such faith in a creature.17Specifically…regarding Christianity:
[INDENT]To believe in Jesus Christ, the Son of God
151 For a Christian, believing in God cannot be separated from believing in the One he sent, his “beloved Son”, in whom the Father is “well pleased”; **God tells us to listen to him.**18 The Lord himself said to his disciples: "Believe in God, believe also in me."19 We can believe in Jesus Christ because he is himself God, the Word made flesh: "No one has ever seen God; the only Son, who is in the bosom of the Father, he has made him known."20 Because he “has seen the Father”, Jesus Christ is the only one who knows him and can reveal him.21
[/INDENT]So…if you read these words from the CCC and don’t believe that Christianity is the one true religion…it is because of one or two reasons:God** has not** given you the GRACE to possess the virtue of FAITH
[LEFT]God has given you the GRACE to possess the virtue of** FAITH**…but by your own FREE WILL you have chosen disobedience…versus the first response to God’s GRACE which is** obedience**.
Faith is a human act
[LEFT] 154 Believing is possible only by grace and the interior helps of the Holy Spirit. But it is no less true that believing is an authentically human act. Trusting in God and cleaving to the truths he has revealed is contrary neither to human freedom nor to human reason. Even in human relations it is not contrary to our dignity to believe what other persons tell us about themselves and their intentions, or to trust their promises (for example, when a man and a woman marry) to share a communion of life with one another. If this is so, still less is it contrary to our dignity to “yield by faith the full submission of. . . intellect and will to God who reveals”,26 and to share in an interior communion with him.
155** In faith, the human intellect and will cooperate with divine grace: "Believing is an act of the intellect assenting to the divine truth by command of the will moved by God through grace."27
In my simple “pea sized” brain…it is that simple…God does all the “heavy lifting”…all I have to do is be obedient.
Lastly, “…there is genius in Catholicism…”. (Matthew Kelly–Aussie author, speaker)