It's just Jesus Christ and His apostles never connected those dots; nor did the Holy Spirit inspiring the written scriptures.
That can be said of many theological facts. The Holy Scripture is the written testimony of things that Christ and the apostles said and did, as remembered 10-30 years later by the disciples. It is also a collection of letters written when the apostle writing them could not travel and teach in person; the letters give encouragement and correct errors that occurred in the Church at the time. The Holy Scripture is not, was not intended as, and cannot be a complete theological manual.
It is a gross error of the Protestant to treat the Scripture as a complete rule of faith, the role that Christ intended for the Catholic Church:
I will build my church, and the gates of hell shall not prevail against it. And I will give to [Peter] the keys of the kingdom of heaven. And whatsoever thou shalt bind upon earth, it shall be bound also in heaven: and whatsoever thou shalt loose upon earth, it shall be loosed also in heaven. (Matthew 16:18-19)