missing "and"-- (MW) The untranslated word "and" is used as the conjunction "and," but it also is used to add emphasis ("also") and, In a series, it can be translated as "not only...but also."

Do -- (WW) This helping verb is added to make this a command, but the Greek here is not a command, but the verb's form requires a "should" or a "might."

not -- The negative "not" used here is again the Greek negative of a subjective opinion. The sense is that "you don't want" to do something, not that it isn't done.

be afraid -- "Be afraid" is translated from a Greek word that means "to terrify" and "to put to flight," but in the passive (as here), it means to be put to flight and be frightened. When applied to people, as here, it means to "be in awe of" or "dread." It is not a command, as you would think from the KJV. However, the next word pushes the meaning to "to put to flight."

of --  This word "of" means "from" or "out of" in both location and when referring to a source. It appears before the word for "them which kill." It is the same preposition that is used in the prefix of the word translated as "kill."

those -- The word translated as "those" 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. 

who -- This word is added because the following verb form was changed.

kill -- (WF) "Kill" is translated from a Greek word that means "destroy" more than just "kill." The base word means "to slay" but it has a prefix that means "out of." This has the sense of "kill off," that is, destroy in a more thorough way. When we talk about "destroying" someone, we use it to mean destroying their reputation, the strength of their spirit and ideas as well as physically killing them. This is more the sense here. It is in the form of an adjective, "destroying" acting as an adjective to the article ("the ones destroying").

the -- The word translated as "the" 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. 

body, -- The word translated as "body" means the body, living or dead, or an animal or person. It is the opposite of "spirit" or "mind." It is the physical substance of things, the body of men and animals or of heavenly bodies or groups of people. It also has many of the same additional meanings, such as a "body of evidence" as "body" does in English. Please read this article.

but -- The Greek word translated as "but" joins phrases in an adversarial way. Since it always falls in the second position, translating it as "however" often captures its feeling better.

can --(WF) "Can" is a word indicating having the power or a desire to accomplish something. It is in a form where the subject ("they") acts on themselves. It is not an active verb but a verb adjective, "having power" modifying the article before "kill" that means "the ones." In Greek, it is not a helping or auxiliary verb like "can" is in English.

not -- The negative used here is the Greek negative of a subjective opinion, commands, and requests. The sense is that "you don't want" or "you don't think" to do something, not that it isn't done. This negative applies to following verbal adjective.

kill -- (WF) "Kill" is translated from a Greek word that means "destroy" more than just "kill" because the base word means "slay." This word is actually an infinitive, but becomes an active verb because the helping verb "can" was used earlier. This "kill" is confusing because the same word is translated as "destroy" later in the verse. The Greek source has the sense of "kill off," that is, destroy in a more thorough way. When we talk about "destroying" someone, we use it to mean destroying their reputation, the strength of their spirit and ideas as well as physically killing them. This is more the sense here.

the -- The word translated as "the" 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. 

soul. -- The word translated here as "soul" is a common word in Greek meaning "life," "soul," "consciousness," and "a sense of self." Christ uses it to mean primary the "self" who knows themselves in this life. This is especially clear here where "mind" is contrasted with "body." This Greek word is our source of the English word "psyche." Please read this article.

Rather, -- The word translated as "rather" is the comparative form of the Greek word meaning "very" so the sense is something like "especially," "to a greater degree," or "rather." This word actually appears after the conjunction "but" or "however" that is not translated here.

be afraid -- This "be afraid" is a change from the earlier verb. Again, it is translated from a Greek verb that means "to terrify" and "to put to flight," and it is in the passive, which it means "to be put to flight" and "be frightened." Here. however, it is in a form that indicates you are doing this to yourselves. Unlike the first "fear," it is a command in the present tense.

missing "however"-- (MW) The untranslated word "however" joins phrases in an adversarial way. Since it always falls in the second position, translating it as "however" often captures its feeling better.

of -- There is no "of" justified by the Greek. It is added because the verb meaning "fear" was changed into a noun, "fear."

the One -- The word translated as "the One" is the Greek definite article, "the," 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. 

who -- (IW) This word is inserted because the following word was changed from the form of an adjective to an active verb.

can -- (WF) "Able" is a word indicating having the power or a desire to accomplish something. It is in a form where the subject ("they") acts on themselves. It is not an active verb but a verb adjective, "having power" modifying the previous article, "the ones."

destroy -- (CW) "Destroy" is translated from a Greek word that means "destroy" more than just "kill" because the base word means "slay."  This word idea translated as "kill" earlier in the verse. The Greek source has the sense of "kill off," that is, destroy in a more thorough way. When we talk about "destroying" someone, we use it to mean destroying their reputation, the strength of their spirit and ideas as well as physically killing them. This is more the sense here.

both -- The Greek word translated as "both" is used as the conjunction "and," the same as the "and" below, but it also is used to add emphasis ("also") and, In a series, it can be translated as "not only...but also."

soul -- The word translated here as "soul" is a common word in Greek meaning "life," "soul," "consciousness," and "a sense of self." Christ uses it to mean primary the "self" who knows themselves in this life. This is especially clear here where "mind" is contrasted with "body." This Greek word is our source of the English word "psyche." Please read this article.

and -- The Greek word translated as "and" is used as the conjunction "and," but it also is used to add emphasis ("also") and, In a series, it can be translated as "not only...but also."

body -- The word translated as "body" means the body, living or dead, or an animal or person. It is the opposite of "spirit" or "mind." It is the physical substance of things, the body of men and animals or of heavenly bodies or groups of people. It also has many of the same additional meanings, such as a "body of evidence" as "body" does in English. Please read this article.

in -- The word translated as "in" also means "within" or "among."

hell. -- (WW) The word translated as "hell" was the name of an area where a constant fire was kept for disposing of trash from Jerusalem. This area was originally where children were sacrificed to Baal, or may have been. See this article on the words for "hell."