A MAN BECOMES AN IGNATIAN BECAUSE THE ONE TRUE RELIGION IS THAT INSTITUTED BY OUR LORD JESUS CHRIST WHICH IS FOUND TODAY IN THE ONE HOLY CATHOLIC AND APOSTOLIC CHURCH
For us who listen to the daily sound-waves of the “Dictatorship of Relativism”, this truth is as dramatic as a sudden bolt of lightning from a clear blue sky.
The Second Vatican Council, in line with 2,000 years of unbroken tradition, when dealing with the question of the true religion, taught:
“We believe that this one true religion continues to exist in the Catholic and Apostolic Church, to which the Lord Jesus entrusted the task of spreading it among all people. Thus, he said to the Apostles: ‘Go therefore and make disciples of all nations baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you’ (Mt 28: 19-20). Especially in those things that concern God and his Church, all persons are required to seek the truth, and when they come to know it, to embrace it and hold fast to it”. (Vatican Council II, Declaration Dignitatis humanae, 1)
We as Catholics recognize that there is only one Church, the One Holy Catholic Apostolic Church governed by the Pope, as Vicar of Christ, successor to St.Peter together with the bishops in communion with him.
As Pope Pius XI taught in Mortalium Animos:
“We were created by God, the Creator of the universe, in order that we might know Him and serve Him; our Author therefore has a perfect right to our service. God might, indeed, have prescribed for man’s government only the natural law, which, in His creation, He imprinted on his soul, and have regulated the progress of that same law by His ordinary providence; but He preferred rather to impose precepts, which we were to obey, and in the course of time, namely from the beginnings of the human race until the coming and preaching of Jesus Christ, He Himself taught man the duties which a rational creature owes to its Creator: “God, who at sundry times and in divers manners, spoke in times past to the fathers by the prophets, last of all, in these days, hath spoken to us by his Son.”
“From which it follows that there can be no true religion other than that which is founded on the revealed word of God: which revelation, begun from the beginning and continued under the Old Law, Christ Jesus Himself under the New Law perfected.
“Now, if God has spoken (and it is historically certain that He has truly spoken), all must see that it is man’s duty to believe absolutely God’s revelation and to obey implicitly His commands; that we might rightly do both, for the glory of God and our own salvation, the Only-begotten Son of God founded His Church on earth. Further, We believe that those who call themselves Christians can do no other than believe that a Church, and that Church one, was established by Christ; but if it is further inquired of what nature according to the will of its Author it must be, then all do not agree.
“A good number of them, for example, deny that the Church of Christ must be visible and apparent, at least to such a degree that it appears as one body of faithful, agreeing in one and the same doctrine under one teaching authority and government; but, on the contrary, they understand a visible Church as nothing else than a Federation, composed of various communities of Christians, even though they adhere to different doctrines, which may even be incompatible one with another.
“Instead, Christ our Lord instituted His Church as a perfect society, external of its nature and perceptible to the senses, which should carry on in the future the work of the salvation of the human race, under the leadership of one head, with an authority teaching by word of mouth, and by the ministry of the sacraments, the founts of heavenly grace; for which reason He attested by comparison the similarity of the Church to a kingdom, to a house, to a sheepfold, and to a flock.
“This Church, after being so wonderfully instituted, could not, on the removal by death of its Founder and of the Apostles who were the pioneers in propagating it, be entirely extinguished and cease to be, for to it was given the commandment to lead all men, without distinction of time or place, to eternal salvation: “Going therefore, teach ye all nations.”
“In the continual carrying out of this task, will any element of strength and efficiency be wanting to the Church, when Christ Himself is perpetually present to it, according to His solemn promise: “Behold I am with you all days, even to the consummation of the world?”
“It follows then that the Church of Christ not only exists to-day and always, but is also exactly the same as it was in the time of the Apostles, unless we were to say, which God forbid, either that Christ our Lord could not effect His purpose, or that He erred when He asserted that the gates of hell should never prevail against it.” (Pope Pius XI, Mortalium Animos, n. 6)
As Pope Pius XII taught in Mystici Corporis Christi:
“When one reflects on the origin of this doctrine, there come to mind at once the words of the Apostle: “Where sin abounded, grace did more abound.” All know that the father of the whole human race was constituted by God in so exalted a state that he was to hand on to his posterity, together with earthly existence, the heavenly life of divine grace. But after the unhappy fall of Adam, the whole human race, infected by the hereditary stain, lost their participation in the divine nature, and we were all “children of wrath.”
But the all-merciful God “so loved the world as to give His only-begotten Son,” and the Word of the Eternal Father with the same divine love assumed human nature from the race of Adam – but as an innocent and spotless nature – so that He, as the new Adam, might be the source whence the grace of the Holy Spirit should flow unto all the children of the first parent. Through the sin of the first man they had been excluded from adoption as children of God; through the Word incarnate, made brothers according to the flesh of the only-begotten Son of God, they receive also the power to become the sons of God.
As He hung upon the Cross, Christ Jesus not only appeased the justice of the Eternal Father which had been violated, but He also won for us, His brethren, an ineffable flow of graces. It was possible for Him of Himself to impart these graces to mankind directly; but He willed to do so only through a visible Church made up of men, so that through her all might cooperate with Him in dispensing the graces of Redemption.
As the Word of God willed to make use of our nature, when in excruciating agony He would redeem mankind, so in the same way throughout the centuries He makes use of the Church that the work begun might endure. 
“If we would define and describe this true Church of Jesus Christ – which is the One, Holy, Catholic, Apostolic and Roman Church  – we shall find nothing more noble, more sublime, or more divine than the expression “the Mystical Body of Christ” – an expression which springs from and is, as it were, the fair flowering of the repeated teaching of the Sacred Scriptures and the Holy Fathers. […]
“Actually only those are to be included as members of the Church who have been baptized and profess the true faith, and who have not been so unfortunate as to separate themselves from the unity of the Body, or been excluded by legitimate authority for grave faults committed. “For in one spirit” says the Apostle, “were we all baptized into one Body, whether Jews or Gentiles, whether bond or free.” As therefore in the true Christian community there is only one Body, one Spirit, one Lord, and one Baptism, so there can be only one faith. And therefore, if a man refuse to hear the Church, let him be considered – so the Lord commands – as a heathen and a publican.  It follows that those who are divided in faith or government cannot be living in the unity of such a Body, nor can they be living the life of its one Divine Spirit.” […]
“As you know, Venerable Brethren, from the very beginning of Our Pontificate, We have committed to the protection and guidance of heaven those who do not belong to the visible Body of the Catholic Church, solemnly declaring that after the example of the Good Shepherd We desire nothing more ardently than that they may have life and have it more abundantly. Imploring the prayers of the whole Church We wish to repeat this solemn declaration in this Encyclical Letter in which We have proclaimed the praises of the “great and glorious Body of Christ” and from a heart overflowing with love We ask each and every one of them to correspond to the interior movements of grace, and to seek to withdraw from that state in which they cannot be sure of their salvation. For even though by an unconscious desire and longing they have a certain relationship with the Mystical Body of the Redeemer, they still remain deprived of those many heavenly gifts and helps which can only be enjoyed in the Catholic Church. Therefore may they enter into Catholic unity and, joined with Us in the one, organic Body of Jesus Christ, may they together with us run on to the one Head in the Society of glorious love. Persevering in prayer to the Spirit of love and truth, We wait for them with open and outstretched arms to come not to a stranger’s house, but to their own, their father’s home.” (Pius XII, Mystici Corporis Christi, 12-13, 22, 103)