2nd Timothy 2:19, “Nevertheless the foundation of God standeth sure, having this seal, The Lord knoweth them that are his. And, Let every one that nameth the name of Christ depart from iniquity.”
No one "falls" into any sin, we all choose to do right or wrong. Proverbs 4:23, “Keep thy heart with all diligence; for out of it are the issues of life.” A believer can sink to the lowest level of sin. Proverbs 14:14, “The backslider in heart shall be filled with his own ways: and a good man shall be satisfied from himself.”
Romans 5:20 teaches that “where sin abounded, GRACE DID MUCH MORE ABOUND.” So the believer is safe in Christ, regardless of sinful choices, but 2nd Corinthians 5:10-11 warns that every believer will be held accountable at the Judgment Seat Of Christ for the good and bad done in the body. Choosing to sin is always wrong. ...
“Christians can never sin cheaply; they pay a heavy price for iniquity. Transgression destroys peace of mind, obscures fellowship with Jesus, hinders prayer, brings darkness over the soul; therefore be not the serf and bondman of sin.” ―Pastor Charles H. Spurgeon, 'Morning And Evening: Daily Readings'