Indefectibility means that the Church remains and will remain the Institution of Salvation, founded by Christ, until the end of the world.
Is. 9:6-7 – For to us a child is born, to us a son is given; and the government will be upon his shoulder, and his name will be called “Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace”. 7 Of the increase of his government and of peace there will be no end, upon the throne of David, and over his kingdom, to establish it, and to uphold it with justice and with righteousness from this time forth and for evermore. The zeal of the LORD of hosts will do this.
Dan. 2:44 – And in the days of those kings the God of heaven will set up a kingdom which shall never be destroyed, nor shall its sovereignty be left to another people.
Dan. 7:14 – And to him was given dominion and glory and kingdom, that all peoples, nations, and languages should serve him; his dominion is an everlasting dominion, which shall not pass away, and his kingdom one that shall not be destroyed.
Mt. 7:24-25 – Every one then who hears these words of mine and does them will be like a wise man who built his house upon the rock; 25 and the rain fell, and the floods came, and the winds blew and beat upon that house, but it did not fall, because it had been founded on the rock.
Mt. 16:18-19 – And I tell you, you are Peter, and on this rock I will build my church, and the powers of death shall not prevail against it. 19 I will give you the keys of the kingdom of heaven, and whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven”.
Mt. 18: 17 – If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, let him be to you as a Gentile and a tax collector.
Mt. 28:19-20 – ” 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, 20 teaching them to observe all that I have commanded you; and lo, I am with you always, to the close of the age”.
Lk. 1:32-33 – He will be great, and will be called the Son of the Most High; and the Lord God will give to him the throne of his father David, 33 and he will reign over the house of Jacob for ever; and of his kingdom there will be no end.
Jn. 14:16 – And I will pray the Father, and he will give you another Counselor, to be with you for ever….
Jn. 14:26 – But the Counselor, the Holy Spirit, whom the Father will send in my name, he will teach you all things, and bring to your remembrance all that I have said to you.
Jn. 16:13 – When the Spirit of truth comes, he will guide you into all the truth; for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come.
1 Tim 3:15 – if I am delayed, you may know how one ought to behave in the household of God, which is the church of the living God, the pillar and bulwark of the truth.
St. Irenæus of Lyon [AD 180-199]The preaching of the Church continues without change and is everywhere the same, and has the testimony of the Prophets and the Apostles and all their disciples. …That in which we have faith in a firm system directed to the salvation of men; and, since it has been received by the Church, we guard it. Constantly it has youth renewed by the Spirit of God, as it were some precious deposit in an excellent vessel; and it causes the vessel containing it to be rejuvenated. (Against heresies, 3, 24, 1)