Simply because I have a brief moment of terrified doubt in the existence of God or something doesn't mean that I don't still believe in him or his church.
But if you have doubts in the existence of God, you can read Bible, and your doubts will disappear, or at least reduce. The more you read Bible, the more doubts become smaller and smaller. Whereas if you have doubts in believing in the necessity of Pope, you read... what?
Here is an example, which shocked me, in which Archbishop gave no answers to questions of teacher of his youth, whom he loved:Declarations and Letters on the Vatican Decrees 1869-1887
(p. 137) Archbishop of Munich and Freising Antonius von Steichele to Döllinger, 1878, 1879, 1886
...I feel myself impelled to put this gift into your hands also as a souvenir, Most Reverend Provost, the teacher of my youth, towards whom I have always preserved my earlier admiration and sense of gratefulness. ...
...Tomorrow you will celebrate your eightieth birthday. I hail this day with heartfelt sympathy. It is with the thankfulness of a pupil to the hoary-headed teacher, with the respect of a disciple for the honoured bearer of the richest knowledge, and with the love of an anxious bishop for the brother who unfortunately is not yet at one with him in that which is highest and most important, that I shall be hovering about you in the spirit to-morrow. ... for what gift of God could I pray more sincerely and heartily for you than for the grace that His lamp and His staff may lead you back to unity with that Church ... and to the consolation of the Holy Church, separated from unity with which, the isolated soul can surely never find rest and peace. ...
...There are but few days which pass without my thinking of you with the old love and sympathy, and without my soul being moved with anxiety and prayer for your welfare and salvation. To-day, the eve of the festival of your name-day, which you will keep to-morrow, offers me an opportunity of bearing testimony to my feelings. I too shall celebrate this festival with you, though I am sorry I cannot do so with unalloyed joy. It is tarnished by the thought that I cannot reach you the hand of brotherly love to mutual endeavours for Christ and His kingdom, that the respected teacher stands here and the grateful pupil there, that of all who are entrusted to his care the bishop must see just that one afar off whom with the love and warmth of his heart he would like to see nearest. It is this feeling which admonishes and urges your bishop to address a few friendly and well-intentioned words to his dear brother, inviting and begging him to be reconciled to the Holy Catholic Church for which he was once so ardent, and for which he has worked by spoken and written words and actions that have been so richly blessed; he also begs him further to re-enter that communion in which he once felt such happiness.
Within the last few weeks, respected Provost, you have made such friendly advances and shown such good-will towards me on occasions of our meeting, that I make this appeal to you with courage and confidence. God has added an almost unusual number of days to the term of your life, and wonderfully blessed you with strength of body and mind. But who knows how long the days of grace for returning into the bosom of the Church will still be granted to you? ...
Döllinger to Archbishop von Steichele, March 1st, 1887
<Long letter in seventeen pages, in which he briefly explains his main thoughts and arguments>
Archbishop von Steichele to Döllinger, March 19th, 1887
Reverend Provost and Reichsrath, - In your letter to me ofthe 1st inst., among other things you say: "I cannot help conjecturing that your Grace has addressed your letter to me at the instigation of colleagues, or because you were moved to it by influence from abroad." This passage of your letter requires a correction. Rest assured that I did not take that step at the instigation of colleagues, or because I was moved to it by influence from abroad. The thought of once more addressing myself to you sprang from my own heart; I carried it out with the feeling of my duty, and out of love to you. You must kindly excuse my entering into details on any other points of your letter. Always bearing the same love to you. - I remain, yours truly,
Archbishop of Munich and Freising.