Proverbs 28:18 Whoso walketh uprightly shall be saved: but he that is perverse in his ways shall fall at once.
This is a conditional promise: if you walk uprightly you will be saved. The condition of walking uprightly signifies God-fearing believers. Jesus walked uprightly for us, and by faith in Christ we are accounted righteous. Thus we shall be saved. “Believe on the Lord Jesus Christ and thou shalt be saved.”
Saved from what? From our deadly enemies: sin, death, and the devil, and from the eternal punishment in hell. Specifically, we are saved from falling, according to the antithetical parallelism of this verse. “The one who is perverse in his ways shall fall at once.” This is the unbeliever, who has rejected or ignored God. He remains in his sin (perversity). Like Adam, he falls immediately, “at once:” “In the day that you eat of it you shall surely die.” Neither Adam, nor the perverse sinner like us, notices immediately how far we have fallen into death right away. Unless the perverse hear the Word of God, they do not realize they are already dead.
Every sin causes us to “fall at once.” When Jesus forgives sin He gives the life to stand upright, and we are saved. Sin and salvation, death and life, is not a never-ending cycle but a continuous upward climb with fits and starts. That is salvation.