Dr. Steve Spurlin
Cornerstone Bible Church
In our last post we delved into two of the three main difficulties that a Christian faces in the daily challenge of living life in obedience to the Holy Spirit, otherwise known as the spiritual, or Spirit-filled life. We will now look at the third aspect of this triumvirate of problems the Christian faces.
The Internal Struggle
It is this environment of maintaining the proper motivation in the Christian life, and overcoming the various impediments into which a new creation is placed (2 Cor. 5:17) and the new man is born. The inner tension that Paul warned about in Galatians 5:16-17 exists between the Spirit and the flesh, or the new creation and the sin nature of the old creation. To use different biblical terminology it is the struggle between the new man (creation) and the old man. That term, "old man," directs our attention back to Romans 6:6. The New American Standard Bible reads, "knowing this that our old self was crucified with Him." However, the Greek uses the exact phrase "old man" (palaios anthropos) in place of "old self." In the act of co-crucifixion we are transferred from our natural born position in the first Adam to our new position in the Last Adam (Rom. 5:12-21, cf. Col. 1:13-14). Paul's further testimony concerning his own struggles is helpful. The Holy Spirit found it necessary to have Paul describe these struggles in order for believers to understand that the new position in Christ does not eradicate the old man in the present. In fact, we should remember Paul's emphatic exclamation at his own plight, "Wretched man that I am! Who will set me free from the body of this death?" (Rom. 7:24) This statement alone illustrates the fact that the sin nature, the old man, the flesh is indeed somehow intrinsically tied to our current physical state. It is our inheritance from the first Adam and cannot be expunged from this present body, but it is the complete removal of this nature to which we look with anticipation.
With the new man born in the believer the internal struggle begins in earnest. This is not to say that we are schizophrenic or possessed of two personalities. Ryrie offers an excellent explanation of the unity of the believer:
Although man is a many-faceted being, and even though these facets of man participate in the conflict between the old and new natures when a person becomes a believer, still man is a unity and acts as one. What I do, I do, not a part of myself....True, certain aspects of my being may originate an action, but that action is performed by me, not part of me....
Galatians 2:20...says not only that Christ lives in me but that Christ lives in me, and the life is a life which I live—to be sure by faith—but nevertheless I live it. Whatever is done, whether for good or evil, I do, for there is no other way for the old nature, the new nature, the soul, the spirit, or any other aspect of my being to express itself than through me. 
It is within the context of this internal battle that the following is issued: "...[L]ay aside the old self,...and put on the new self..." (Eph. 4:22, 24). Our new position in Christ means that positionally, the old man is put off. The everyday experience, or our experiential or progressive sanctification, is where the battle to live the Christian life takes place, and the old man will not go quietly. We must actively, and consistently strive to put off the old man, and replace him with the new man, the man who is to be transformed by the renewing of his mind (Rom. 12:2), replacing the old way of thinking with "the mind of Christ" (1 Cor. 2:16) to which every believer has access.
The victory of the new man over the old man is, on the part of the believer, dependent upon a positive volitional response to biblical commands such as the one just mentioned. In a word, victory for the new man over the old is through obedience. The power to make the correct decision is provided by the Spirit, "for it is God who is at work in you, both to will and to work for His good pleasure" (Phil. 2:13). Therefore, the desire is produced by the new man in conjunction with the divine enablement of the Spirit, the positive volition belongs to the believer, but the power to overcome belongs to the Lord.
It is clear from what we've seen that there is a great deal for the believer to overcome. Between the various impediments that the multiple enemies place in his way and the internal struggle that is faced on a moment-by-moment basis the battle is seemingly hopeless for the believer. Yet, God has not left believers to fend for themselves. The indwelling Spirit provides the power for the believer's victory and progress in the Christian life.
 Ryrie, Christian Life, 32-33.