By faith, so if you loose that faith, you naturally loose justification. Justified by faith in believing in the shedding of Jesus's blood.
Rom 5:9 - Much more then, having now been justified by His blood, we shall be saved from wrath through Him. 3:25 - God presented Him as the atoning sacrifice through faith in His blood,
2 Tim 2:11,12 - This is a faithful saying: For if we died withHim,We shall also live withHim. If we endure, We shall also reign withHim. If we deny Him, He also will deny us.
Endure in faith.
Phil 3:9 - and be found in Him, not having my own righteousness, whichisfrom the law, but that whichis through faith in Christ, the righteousness which is from God by faith;
If you loose, drop your faith = no righteousness, so there is no once saved always saved there.