Here, though you cannot see it in English translation, Jesus starts to address an individual personally. We may assume from the last verse,  Luke 22:3, that this is Simon, though the "you" in that verse was plural. 

The Greek word translated as "but" means "but", "however", and "on the other hand". Since it always falls in the second position, translating it as "however" often captures its feeling better. 

The pronoun "I" is used here. Since, as the subject of the sentence, it is part of the verb, its explicit use accentuates who is speaking "I." Saying "I myself" captures this feeling in English. We have seen this emphasis several times at the Passover meal.

The Greek word translated as "have prayed" is means to "lack", "miss", "stand in need of", "want",  "to be in want or need", "require", and to "beg a thing from".  It is an uncommon word for Jesus. It is not a command, as translated, but a passive verb, "I am wanting".   The form is not the past tense, as translated, but a tense that refers to a specific point in time, past, present, or future.

The Greek word translated as "for" means It means "around" when referring to a place, but, in this context, it means "about", "concerning", "on account of," and "in regard to." This is the way Christ usually uses it.

The word translated as "thee" is singular form of the second person pronoun. This is the first time Jesus has used the singular in this group of verses. Though he has been likely answering questions that whole time, his answers, until now, have addressed everyone.

The word translated as "that" is an adverb or a conjunction that starts a subordinate clause "there", "where," and "in order that."

The word translated as "thy" is the possessive form of the second-person, singular pronoun.

The term translated as "faith" is closer to our idea of having confidence or trust in people, especially their word, rather than having religious belief. This noun follows the verb, which creates some suspense in the verse.

The key word here is translated as "fail". The verb is a rare one for Jesus, only used here and one other place. It seems chosen for the humor. The word primarily means to "forsake", "desert", "abandon" not "fail".

The negative used here is the Greek negative of a subjective opinion, commands, and requests. The sense is that "it doesn't want" to do something, not that it isn't done or don't think something that might be true. This negative begins the clause, coming before the verb and the subject.

The Greek word translated as "and" is used as the conjunction "and", but it also is used to add emphasis ("also").

The "when"  is from an adverb meaning "when", "at what time", "at some time or other", "at some unknown time, and "at some time in the future."

The "thou" here is the pronoun. Since pronouns are not usually used for subject in Greek, its use is to accentuate the word like we would say "you yourself".

"Art converted, " is translated from a Greek word "to turn about", "return", or "to turn around," but also means "cause to return" and "to turn one's mind towards" something. It is not passive, but active, "you return".

"Strengthen" is a Greek verb that means to "make fast", "prop", "fix"​, and "support".  Jesus only uses this word twice. It is the word that means setting a stone in the ground so it won't move and putting a rainbow in the clouds, but metaphorically, it means "to establish".  The sense here is clearly "support".

The word translated as "thy" is the possessive form of the second person pronoun.

The word translated as "brother" means a biological brother, any kinsmen, and more broadly and friend or associate. .