"...after that ye believed, ye were sealed with that holy Spirit of promise..." KJV
When you become saved, you receive the new nature which comes from the Holy Spirt as a deposit of your future redemption (Ephesians 1:13-14 KJV In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.) The Holy Spirit gives you a new nature that is now in oppostion to your old nature, called the flesh which was your Body and Soul. This warfare between the two means the old isn't reformed because we are now a new creation. This is why as babes, we should desire the sincere milk of the word of God to grow our new nature. Having studied, memorized and fellowshipped around the word, we mature into Christians that can now study the meat of scripture. This allows us to put on the whole armor of God and use the only offensive weapon you have been given, the sword - which is the word of God. (Eph 6:13,17 KJV 13 Wherefore take unto you the whole armour of God, that ye may be able to withstand in the evil day, and having done all, to stand.17 And take the helmet of salvation, and the sword of the Spirit, which is the word of God; Hebrews 4:12 KJV For the word of God is quick, and powerful, and sharper than any twoedged sword, piercing even to the dividing asunder of soul and spirit, and of the joints and marrow, and is a discerner of the thoughts and intents of the heart.) God has provided us grace to account for the flesh winning battles in our behavior but we should always strive for Christian self government to bring honor to God in our ambassador status with Christ.