John 1:1 refers to Jesus as "the Word" and ends, "the Word was God" in all English translations except the New World Translation, in which it ends, "the Word was a god."
The "a" in the New World Translation makes Jesus someone less than the Creator God, but without the "a", Jesus is the Creator God. So the "a" makes a significant difference.
All English New Testaments are translations. If the original Greek text has the "a", intentionally deleting it to make the English translation say "the Word was God" would be a serious sin since it would be twisting the Bible to say that a creature is the Creator God.
And if the original Greek doesn't have the "a", intentionally adding it to make the English translation say "the Word was a god" would also be a serious sin since it would be twisting the Bible to say that the Creator God isn't the Creator God.
As you can see on this page and copied below, the "a" is NOT in the original Greek text of John 1:1.
Therefore, the translators of the New World Translation added the "a" and committed the serious sin of twisting the Bible to say that the Creator God isn't the Creator God.
And the excuse they gave for adding the "a" is revealing. In the clause, "Man bites the dog," English grammar determines the subject and the object by the order of the nouns relative to the verb, from the left to right. Because "man" comes before the verb, it is the man who bites the dog, not the dog biting the man. In Greek grammar, a noun in the nominative is typically the subject of a clause. But when a clause is equating two nouns, both of which are in the nominative, Greek grammar places the article (eg. "ho" (the) boxed in red below from this page) in front of only the subject to identify it as the subject of the clause. In the red box below, the "N-NMS" designations under both "God" and "Word" indicate both words as "Noun - Nominative Masculine Singular." To identify "Logos" (Word) as the subject of the clause, the article "ho" (the) is placed in front of only "Logos" (Word). Another article is not placed and should not be placed in front of "Theos" (God) because it is the predicate, not the subject, of this clause, the correct translation of which is, "The Word was God."
The translators of the New World Translation claimed that the indefinite article "a" needs to be inserted in front of "god" in English because "Theos" (God) is not preceded by an article in the original Greek. But three evidences refute both the veracity and the sincerity of their claim.
First, the notion that the absence of the article before a Greek noun requires the insertion of an indefinite article in English is farfetched to anyone who knows anything about Greek grammar.
Second, if they sincerely believed their own claim, they at least would have translated the clause from left to right as usual as, "a God was the Word." The fact that they recognized "Logos" (Word) as the subject of the clause even though it comes after the verb and recognized "Theos" (God) as the predicate even though it comes before the verb and correctly reversed their order in their English translation indicates that they were well aware that the absence of the article before "Logos" (Word) was to identify it as the predicate of the clause, not to suddenly require the insertion of an indefinite article in English.
Third, after John 1:1, the word "God" next appears in John 1:6, which the New World Translation translates as, "There came a man who was sent as a representative of God; his name was John." Since there is no article in front of the Greek word for "God" in this verse either, if they sincerely believed that its absence requires inserting an indefinite article in English, they would have inserted it here as well to make it say "of a God." As you can see, they did not, and it reads, "of God." Thereafter, the word for "God" next appears in John 1:13, which the New World Translation translates as, "And they were born, not from blood or from a fleshly will or from man’s will, but from God." Since there is no article in front of the Greek word for "God" in this verse either, if they sincerely believed that its absence requires inserting an indefinite article in English, they would have inserted it here as well to make it say "from a God." As you can see, they did not, and it reads, "from God." Thereafter, the word for "God" next appears in John 1:18, whose first sentence the New World Translation translates as, "No man has seen God." Since there is no article in front of the Greek word for "God" in this verse either, if they sincerely believed that its absence requires inserting an indefinite article in English, they would have inserted it here as well to make it say "seen a God." As you can see, they did not, and it reads, "seen God." So their claim that the absence of the article requires inserting the indefinite article "a" in front of the word for "God" in John 1:1 in English is contradicted by their own translations before they makes it out of even just the first chapter of John.