Saints, when they are walking in the flesh, instead of walking in the Spirit are sinners.
Wrong! A person doesn't go from being an (adopted) child of God to not being a child of God. A person is a saint (meaning sanctified) even if s/he sins. S/he does not lose their status as a child of God.
Of course, there is a sin that leads to death, but that is not what is being discussed.
1 John 5:16-17, "If you see any brother or sister commit a sin that does not lead to death, you should pray and God will give them life. I refer to those whose sin does not lead to death. There is a sin that leads to death. I am not saying that you should pray about that. All wrongdoing is sin, and there is sin that does not lead to death."