It's added for flow because of translator bias. It's purposely put into parenthesis to show that it's NOT part of the greek...to show that it's added. However, the flow, the bias, is entirely up to the translator and is not inspired.
Spirits are not material, and are indeed eternal.
In a general sense that's true. But what are you referring to?
Do you disagree that eternal life is a gift of God and that the fate of sinners is death?
Rom 6:23 For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.
BTW, I don’t waste my time with so-called ‘modern’ ‘translations,’ since they were all based on the unbelievers Wescott and Hort’s revival of deliberately corrupted texts Vaticanus and Sinaiticus, that were produced by the mischief of Clement and Origen.
I prefer the King James and the NASB. I will bring up other translations though to show that scripture translation is entirely up to the biases of the interpreters.
All of the dead inhabitants of the Earth are presently reduced to spirits. Only those that believed will be given bodies that permit them to again live. The rest will spend eternity as spirits without life or bodies, in tourment.
"Do you disagree that eternal life is a gift of God and that the fate of sinners is death?"
Not at all. Life requires a body, which will be given to those that believed.