missing "but"  -- (MW) The untranslated word "but" means "but," "however," and "on the other hand." It joins phrases in an adversarial way. Since it always falls in the second position, translating it as "however" often captures its feeling better.  It can also be an explanation of cause ("so").

I  -- 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.

missing "myself" -- (MW)  The subjective pronoun repeats the information in the verb so it should be repeated in English like "I myself."

have -- The word translated as "have" means to "have," "possess," "bear," "keep close," "have means to do,"  "to have due to one," or "keep" and many specific uses. This verb isn't used to form past tenses as it is in English.

missing "the"  -- (MW) The untranslated word is the Greek definite article, which usually precedes a noun and, without a noun, takes the meaning of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those"). See this article for more. 

testimony- "Testimony" is from a Greek word that means "testimony" and "evidence."

weightier -- (CW) "Weightier is an adjective that is the comparative form of the word meaning "big" or "great." It means "bigger," "higher," "longer," "greater" and simply, "superior."

than --   This word "than"  comes from the genitive case of the following word that requires the addition of a preposition in English.  The most common is the "of" of possession. However, it can also mean "belonging to," "part of," "which is," "than" (in comparisons), or  "for," "concerning" or "about" with transitive verbs.

that -- The word translated as "that" is the Greek definite article, without a noun, it has the sense of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those") than the English "the." See this article for more. 

of --   This word "of"  comes from the genitive case of the following word that requires the addition of a preposition in English.  The most common is the "of" of possession.

John: -- --  "John" is the Greek word translated as the English proper name.

For --The word translated as "for" introduces a reason or explanation so "because" and, in questions, "why." However, since this word always appears in the second position, it is more like an aside remark like, "consequently" or "as a cause." 

the  - -  The word translated as "the" is the Greek definite article, without a noun, it has the sense of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those") than the English "the." See this article for more. 

works -- The Greek word translated as "works" means "deeds," "actions," and "things" in the sense of "every thing."

that-- The word translated as "that" is a demonstrative pronoun ("this" "that"), but it often acts as a pronoun ("the one that), especially a connective pronoun ("the one that") introducing a dependent clause.

the   -- The word translated as "the" is the Greek definite article, without a noun, it has the sense of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those") than the English "the." See this article for more. 

Father -- "Father" is the Greek noun that means "father" or any male ancestor so "forefathers." It is the word that Christ uses to address his own Father.

has -- This helping verb "has" indicates that the verb is the tense indicating an action completed in the past.

given -- The verb translated as "given" means "to give," "to grant," "to hand over," "appoint," "establish," and "to describe." It is almost always translated as some form of "give."

me -- The "me" is in the indirect object form on the first-person pronoun, so usually "to me," though the form has other uses in Greek.

missing "that"  -- (MW) The untranslated word "that" is an adverb "in that place," "there," "where," "when," or as a conjunction that starts a subordinate clause  "that," "when," "in order that" or "because."

to -- (WF) This "to" is added because the infinitive form of the verb requires a "to" in English. However, this is an active verb in the first-person, subjective form.

missing "should" or "might"-- (MW) A helping verb is necessary because the following verb is a verb of possibility, a subjunctive, something that "should" or "might" occur. The helping verb is not needed in a clause beginning with an "if" or a "when."

finish, - - As a verb, the word translated as "finish" means "to make perfect", "to make complete", "make perfect", "to bring to consummation," and "to bring fruit to maturity." It would be in the form where the subject acts on themselves, "you might make yourself perfect."

missing "them"  -- (MW) The untranslated word"his" is the Greek word commonly translated as third-person pronouns in English.

the -- The word translated as "the" is the Greek definite article, without a noun, it has the sense of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those") than the English "the." See this article for more. 

very -- The word translated as "very " is the Greek word commonly translated as third-person pronouns in English.  The word means "the same" when used as an adjective.

works -- The Greek word translated as "works" means "deeds," "actions," and "things" in the sense of "every thing."

that -- The word translated as "that" is a demonstrative pronoun ("this" "that"), but it often acts as a pronoun ("the one that), especially a connective pronoun ("the one that") introducing a dependent clause.

I -- This is from the first-person, singular form of the verb.

am - -- This helping verb indicates the present tense of the verb.

doing, -- The Greek word translated as "do" has the primary meaning of "making" or producing" something or "causing" or "performing" as service. It describes a productive action.  It is not as broad a word as the English "do," which covers all actions, productive or not.

testify --  "Testify " is the Greek verb that means "to give testimony" and "to bear witness." It has the sense of being true testimony. It is the verb form of the Greek word for "testimony" and "proof," which is the source of our word "martyr," and its funny spelling.

missing "about"  -- (MW) The untranslated word  means "about" when referring to a subject, it means "about," "concerning," "on account of," and "in regard to." This is the way Jesus usually uses it. This is not the common "of" from the possessive, genitive form of a word.

missing "me"  -- (MW) The untranslated word is the first-person possessive singular pronoun. This is the form taken by the preposition.

that -- The word translated as "that" introduces a statement of fact or cause, "for what," "because," "since," and "wherefore."

the   -- The word translated as "the" is the Greek definite article, without a noun, it has the sense of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those") than the English "the." See this article for more. 

Father -- "Father" is the Greek noun that means "father" or any male ancestor so "forefathers." It is the word that Christ uses to address his own Father.

has-- This helping verb "has" indicates that the verb is the tense indicating an action completed in the past.

sent -- The "sent" here is a word that means "to send off" and "dispatch." It is the source of our word "apostle."

me. -- "Me" is the regular first-person pronoun in Greek as the object of the verb or preposition.