[John Leland 1789]

“Jesus established one Church(John 17:22-23).”

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If that church is described in John 17, then it consists of all those in who Christ dwells. You have provided the verse.

Many don't have a favorable opinion of Christians who can say positively in great faith that they KNOW that they are saved and that Christ dwells within. Am I correct to state that Catholicism teaches that one can not really know until death?

The Church of which Christ was made Head when God raised Him from the dead and sat Him at His own right Hand far above all heavens (Ephesians 1), is not something dependent upon any earthly head, edifices, sacraments or ordinances performed with men's hands, earthly priesthoods, costumed clergy (or any clergy, for that matter). It cannot be entered through any earthly church or organization. Not one I might belong to, not one you might belong to, no earthly thing.

[Mad Dawg]

Am I correct to state that Catholicism teaches that one can not really know until death?

On the Contrary:

Here is what Saint Dominic de Guzman said as his death approached:

“Don’t worry, in heaven I shall be of much more use to you than I am now,...”

Similarly, Therese of Lisieux said:

"My mission - to make God loved - will begin after my death," she said. "I will spend my heaven doing good on earth. I will let fall a shower of roses."