Nothing is stated in the Bible about mankind having two natures. Genesis 2:7 teaches that God made man from the dust of earth then breathed life into him. Man became a living soul. Soul = Body + Breath of life. He did not receive a soul with two natures. In fact, both the children of Adam and animals are of the earth and share the same fate, death. Ecclesiastes 3:19,20(RSV), "For the fate of the sons of men and the fate of beasts is the same; as one dies, so dies the other. They all have the same breath, and man has no advantage over the beasts…All go to one place; all are from the dust, and all turn to dust again."
If a man accepts Jesus as his Savior and then sacrifices his life to do God's will, things change. When God adopts him into His family as His child, God begets him to a new life with the holy spirit. 1 Corinthians 5:17, "if any man be in Christ, he is a new creature." Romans 8:9 (NASB), "However, you are not in the flesh but in the Spirit, if indeed the Spirit of God dwells in you."
The holy spirit works within our hearts and minds to transform us into Christ-likeness. Romans 12:1,2 (NKJV), "present your bodies a living sacrifice, holy, acceptable to God…And do not be conformed to this world, but be transformed by the renewing of your mind." This process is a constant struggle between our old, sinful man and our new, spiritual creature.
The Apostle Paul said, "Although I want to do good, evil is right there with me. For in my inner being I delight in God’s law; but I see another law at work in me, waging war against the law of my mind and making me a prisoner of the law of sin at work within me. What a wretched man I am!" Romans 7:21-24 (NIV)
God’s holy spirit powerfully influences and assists Christians, who diligently serve Him. They study Scripture, pray, help brethren, families, and mankind. Philippians 2:13 (RSV) assures us of God's help: “for God is at work in you, both to will and to work for his good pleasure."
If faithful, Christians will be resurrected with spirit bodies. 1 Corinthians 15:44, "It is sown a natural body; it is raised a spiritual body. There is a natural body, and there is a spiritual body." Psalm17:15, "As for me, I will see Your face in righteousness; I shall be satisfied when I awake in Your likeness."