Falling in sin is the same as doing sin. It is when you are tempted to sin and knowingly agree to these temptations or desires in your mind, and you let these desires become sinful thoughts, words, and deeds. But if you fall in sin, your overall decision to serve God and overcome sin has not changed. Even though you have made a mistake you still want to live free from sin. A fall is seen as an “only once” event. Living in sin on the other side means that the person doesn’t want to stop sinning.
The expression “the Fall” is not found in the Bible, but it means the first time that mankind (Adam and Eve) gave in to sin in the garden of Eden. By doing that, their human nature became sinful, and this has been passed down to their children and then to all the generations that came after them. (1 John 2:1; Revelation 2:4-5.)