This is the secret in all prayer, even in the case of Jesus himself. It is possible that John has this idea in mind when he applies it to those who reject Jesus Christ as God's Son and set themselves up as antichrists. This sin unto death. He leaves them to God. The world today takes sin too lightly, even jokingly as a mere animal inheritance.
Sin is a terrible reality, but there is no cause for despair.
Sin not unto death can be overcome in Christ. It is a difficult phrase, but this is probably the idea. Here the idea is to touch to harm. This is a terrible picture of the Graeco-Roman world of the first century A.D., which is confirmed by Paul in Romans 1 and 2 and by Horace, Seneca, Juvenal, Tacitus. That is, God.