'Able' in the Bible

Everyone who has been born of God does not sin, because His seed remains in him; he is not able to sin, because he has been born of God.

This is how we will know that we belong to the truth and how we will be able to keep ourselves strong in his presence.

if any one may say -- 'I love God,' and his brother he may hate, a liar he is; for he who is not loving his brother whom he hath seen, God -- whom he hath not seen -- how is he able to love?

Anything which comes from God is able to overcome the world: and the power by which we have overcome the world is our faith.

Who is able to overcome the world but the man who has faith that Jesus is the Son of God?