I think it is prudent to carefully warn all Christians to be very careful how they regard the issue of sin.
Yes, we all sin, there are sins of the flesh, of the mind, premeditated sins, sins of omission, sins of disobedience, breaking a commandment, etc
I think the question is: Does one lead a “lifestyle” of sin. In other words, have they grown so accustomed to perhaps some secret sin, or private sin, or sin “in the closet” so much that their conscience is no longer bothered by it. After all, there are sins that “sneak up” on us, and are what the bible refers to as “sins that so easily beset us”. So a Christian has to be constantly on his/her guard and day by day go forth with the spiritual weapons of breastplate of righteousness, helmut of salvation, etc
Paul wrote in Hebrews about the new covenant versus the old covenant. In the old covenant, it took 2 or 3 witnesses to determine if someone disobeyed the Law of Moses, and if found guilty, the punishment could be death. “Anyone who has set aside the Law of Moses dies without mercy on the testimony of two or three witnesses.
29How much severer punishment do you think he will deserve who has trampled under foot the Son of God, and has regarded as unclean the blood of the covenant by which he was sanctified, and has insulted the Spirit of grace?…” Heb 10:28
For a Christian our lives do not belong to us, really. We live to glorify God. Paul said in Galatians 2:20 "I have been crucified with Christ; and it is no longer I who live, but Christ lives in me; and the life which I now live in the flesh I live by faith in the Son of God, who loved me, and delivered Himself up for me."
Therefore it is more serious when we sin now than it was in the old covenant. "For in the case of Christians who have once been enlightened and then have fallen away ... they again crucify to themselves the Son of God, and put Him to open shame." (Hebrews 6:4-6)
So if a person is truly saved, understand what has happened, feel the freedom and joy in Christ because of the fact that they are no long under condemnation, have the Holy Spirit to guide them and certainly make it clear to them when they do sin (Be sure your sins will find you out), I find it very difficult to believe that a true Christian will pre-meditatively sin IF they were saved to begin with. Humans are not dogs that return to their vomit.
Having said all of this, I believe that I have eternal security. I try (but don't always succeed) to do what Bill Bright of Campus Crusade used to say. He called it "spiritual breathing" where a Christian takes the Holy Spirit with him every day, prays for God's wisdom, asks for forgiveness when mistakes are made, agrees with God not to engage in that activity again, etc. (i.e.: stay "in tune" with God)
So I don't agree with all the article, but some of it. The emphasis on OSAS should be the OS - was that person truly saved? And that is a very difficult determination to make (and shouldn't be made very often, if ever, except by God)