en_tn_condensed/gen/06/03.md

My spirit

Here Yahweh is talking about himself and his spirit, which is the Spirit of God.

flesh

This means that they have physical bodies that will one day die.

They will live 120 years

"They will live one hundred and twenty years." Possible meanings are 1) the normal lifespan of people would decrease to 120 years. Alternate translation: "They will not live more than 120 years" or 2) in 120 years everyone would die. Alternate translation: "They will live only 120 years" (See: rc://en/ta/man/jit/translate-numbers)