Charles Ryrie states, “All believers have the capacity to serve sin and the capacity to delight in the law of God.” This is so because “God has provided the way of victory. But, because [the flesh] has not been refined, it is a powerful enemy with which we have to live.” Since God provided but did not refine, “these two capacities [are] in constant conflict.” Therefore, we will have occasions where the “old nature [will] occasionally erupt” and we will not act as though we are saved.
This does not mean you are not saved though. No, it only means we have a battle, daily, against spiritual forces that want to bring us down. Ephesians 2:2 states that Satan is the prince of the power of the air. He is darkness and wants us to walk in that darkness. 1 John 5:19 says “the whole world lies in the power of the evil one.”
Paul also tells us that we do not battle against flesh and blood but against powers and principalities (Eph. 6:12).
These enemies will use our flesh against us and we may very well falter. Just because you falter and sin, does not mean you are not saved and secure in Christ.
So rest assured that we have an advocate who stands in for us when we fail (1 Tim. 2:5; 1 John 2:1). We can be as Paul was in his struggles and say, “Wretched man that I am! Who will deliver me from this body of death? Thanks be to God through Jesus Christ our Lord! So then, I myself serve the law of God with my mind, but with my flesh I serve the law of sin.” (Rom. 7:24-25).
We have Christ and the Holy Spirit so when we walk in the Spirit we can also say, “There is therefore now no condemnation to those who are in Christ Jesus, who do not walk according to the flesh, but according to the Spirit.” (Rom. 8:1).
Trust in Christ and the guidance of the Spirit and walk according to the Spirit and the old nature and its eruptions will become less and less.
 Ryrie, Charles C. Balancing the Christian Life, (46) Moody, 1976.