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16 If anyone sees his brother committing a sin not leading to death, he shall ask, and God will give him life—to those who commit sins that do not lead to death. There is sin that leads to death; I do not say that one should pray for that. 17 All wrongdoing is sin, but there is sin that does not lead to death.
1 John 5:16-17 (ESV)

As children of God we have confidence in prayer because of our intimate relationship with him (1 John 5:14-15). In love, we pray (1 John 5:16-17) for those who are in sin, but not in deadly sin (literally, "sin unto death"), probably referring to apostasy or activities brought on under the antichrist; cf Mark 3:29; Hebrews 6:4-6; 10:26-31. Even in the latter case, however, prayer, while not enjoined, is not forbidden. The letter concludes with a summary of the themes of the letter (1 John 5:18-20). There is a sharp antithesis between the children of God and those belonging to the world and to the evil one. The Son reveals the God of truth; Christians dwell in the true God, in his Son, and have eternal life.

29but whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin"--