A person who had been saved by grace can fall from grace. The apostle Paul told some Christians in Galatia: “You have fallen away from grace” (Gal 5:4).
Jesus said the believer has (present tense) eternal life (Jn 5:24); however, the believer can become an unbeliever. “Take care, brothers, lest there be in any one of you an evil, unbelieving heart, leading you to fall away from the living God” (Heb 3:12). The unbeliever has nothing but condemnation (Mk 16:16).
Faithful Christians, however, do not fall from grace every time we sin. Recognized sin, of course, must be repented of and we must pray“forgive us our sins” (Lk 11:4). If that is not our attitude toward sin, we are not walking in the light. But when we are walking in the light, God does not wait until we pray to forgive; the blood of Jesus Christ His Son is continually washing our sins away (I Jn 1:7).
For those who are in Christ and who “walk not according to the flesh but according to the Spirit… there is no condemnation” (Rom 8:1-4). David, quoted by Paul, blesses “the man against whom the Lord will not count his sin” (Rom 4:6-8). Paul uses that language and applies it to those who “walk in the footsteps of the faith that our father Abraham had” (Rom 4:12). God does not count his sins because, as he walks in faith he walks in the light and the blood of Jesus is continually cleansing him from sin.