Are there any grammar mistakes in the quote "I am become death, the destroyer of worlds"?

Question

Oppenheimer once said, "I am become death, the destroyer of worlds".

Why did he use an "am" before "become"? Besides, why not use "the world" instead of "worlds"?

Answer 1

Oppenheimer later said of this moment, and of his choice of translation (according to "J. Robert Oppenheimer Explains How He Recited a Line from Bhagavad Gita ..." from Open Culture):

“We knew the world would not be the same,” Oppenheimer remembered in 1965. “A few people laughed, a few people cried. Most people were silent. I remembered the line from the Hindu scripture, the Bhagavad Gita; Vishnu is trying to persuade the Prince that he should do his duty and, to impress him, takes on his multi-armed form and says, ‘Now I am become Death, the destroyer of worlds.'” The translation’s grammatical archaism made it even more powerful, resonating with lines in Tennyson (“I am become a name, for always roaming with a hungry heart”), Shakespeare (“I am come to know your pleasure”), and the Bible (“I am come a light into the world, that whosoever believeth on me should not abide in darkness”).

This line is also mentioned in his New York Times obituary and in this Wired news story

As Oppenheimer correctly notes in his later account, the perfect tenses, in modern usage formed only with the auxiliary verb "to have" ("I have become Death") once used the auxiliary to be with some verbs, including "to become" and "to come" ("I am come at your word"). Many of these archaic forms are included in well-known quotations, and so remain in limited use. People sometimes use such constructions to imitate the tone of or parody such older usages.

Some sources state that Oppenheimer identified the line as a quote when he spoke it on the occasion of the first atomic bomb test. Some say that Oppenheimer who had studied Sanskrit (the original language of the Bhagavad Gita) made the translation, others that he spoke the line as it his teacher had translated it.

In any case Oppenheimer used an old form of the Present Perfect in line with the treatment of the King James Bible and other important older texts.