This kind of very abstract, very formal, very ritualized Latin is the very hardest stuff to read, especially when it is out of context. So don't get discouraged! Rather than worrying about translating (why do you need a translation?), you could focus on getting the main idea - and the main idea is that someone is conveying these "secreta" and they might be good things, or they might be bad things, and if they are bad things, he wants to be forgiven and/or do penance (ut vel indulgentiam merear
vel dignam penitentiam persolvam), but if they are good things, he wants to be told to carry on doing them (ut augere studeam). It is a very very long and very very polite way of not saying much at all - and because it really does not say very much at all, it seems like nonsense, because all these Latin ecclesiastical formulas of politeness are very foreign to us in English.
Translating word for word from Latin into English is not something that is likely to increase your confidence in Latin because translating is HARD - Latin has all kinds of idioms that are peculiar to Latin, it has all kinds of grammatical constructions that are different from English, and it has a whole stylistic range that it takes time to get used to (and translating into English does not really help with that at all).
Just a few cautions:
soli: this is a very tricky word in Latin since it can mean quite different things (although English is full of such things: you wind a watch, but the wind blows, etc. - wind - wind; they look the same but they are different words and even pronounced differently) - anyway, soli is almost certainly the adjective "solus" in the dative singular agreeing with pietati vestrae; it's a good idea to be familiar with that list of adjectives like solus, unus, etc. which look like regular 1st-2nd declension adjectives, but which have irregularities in their declension, like a genitive in -ius, dative in -i (unus, ullus, nullus, uter, neuter, totus, alter, solus)
mihi: don't lose track of that little mihi - after the messenger conveys all the secrets he is support to REPORT back (representare is report back) to me, the sender, the consilium that will comfort the sender in his old age, etc.
paternitatis vestrae: this is just a formal way of speaking, like Your Holiness, Your Fatherness, etc. - it is a very fancy way of saying "your"