Has nothing to do with legalism. Has everything to do with this: (Hebrews 10)
29Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done DESPITE UNTO THE SPIRIT OF GRACE?
....And again, THE LORD SHALL JUDGE HIS PEOPLE.
OSAS/OJAJ is a lie. RAVI ZACHARIAS was the golden poster boy of that lie.
Hebrews 10 is addressed to the entire but exclusive body of humans to which the Mosaic/Davidic Covenant applied up to the moment that God Incarnate pronounced at the moment of His physical death "Tetelestai:" (My work on earth to meet Jehovah's righteous demands is finished! It is done!), and the Torah's law system was abolished.
It was those Hebrews of the Apostles' time , the Jews who were raised in the religious system purportedly governed by the Mosaic law, who upon the death, resurrection, and ascension of the Lord Jesus Messiah/Christ, they now needed to be saved by faith alone in Christ as their Savior and Eternal High Priest, not by the blood of bulls and goats and grain offerings, etc.
The passage you have based this current point on (Heb. 10:29) applies only to the Hebrews of that time who had to make the decision to pledge their allegiance to the Lamb of Calvary and leave the stifling, mis-administered religion of offering of sacrifices that could NEVER take away and utterly remove their own sins and guilt.
This epistle to the dispersed Hebrews had NOTHING to do with the Gentiles of that day or this, so you cannot use it for the proof of your false you-can-lose-your-salvation doctrine to today's Christ-seeking audience.
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I write this, philsworld, not to convince you that your way of thinking is just plain wrong, because I know that I can do that.
Only God in the Holy Spirit now present in the temporal sphere, Whose task is to convict you of your sin, of Jesus' righteousness POSSESSED by those who are really liberated from sin, and that God is judging you even now for your unrelieved contention against His Plan of Salvation and its pursuant holiness, going forward.
No, I am writing this to show that there are faithful servants of The Christ who are contending for The Faith according to /his Scriptural commandment (Jude verse 3), and how that hedge of defense might be lifted up.
One is quite aware that with your false plan of salvation, Scripture says that you, philsworld, cannot receive the deep things of the Spirit of God, because they seem foolish to you, neither can you understand them, because they are spiritually discerned. And it does not seem that you have attained to that state to have the spiritual faculty for it.
But anyone who has been regenerated by full confidence in the saving power, ability, and desire of our Redeemer -- that person who reads what I have written can understand, affirm, and be encouraged by what I have said to you. Otherwise, debating with you is a waste of time.
An OSAS child of God freely and willingly observes God's commandments because doing so pleases Him and results in many rewards, knowing that this activity is NEVER salvific in nature, but brings delight in one'ss fellowship with his/her Heavenly Father and as a servant of the Master.