The old self is out to steal, kill, and destroy our new self. I know it sounds morbid, but it's true. If you have felt yourself being tugged at relentlessly to return to old habits you know are destructive, you have experienced your old self come to take you down.
If you're struggling and wrestling with your old self today, I highly recommend reading through the whole of Romans 8. I initially wanted to just put in here vs. 37, but I don't think it would give a full enough picture of what we have been graciously given in Christ. May God's word give all of us strength to endure and to abide in his love. Amen.