Marshall on the perseverance of the saints

This is something that I have been pondering about lately (very much in fact). There are probably no easy answers, with both the Calvinists and Arminians viewpoints varying so very much. On one hand I guess salvation at the point of conversion is a gift that we freely receive. Yes we cannot do anything to earn our salvation.. But I really wonder is a person truly saved if he behaves in a manner contrary to the standards that God has set in his holy Word? If I fall so short of the indicative markers of what a Christian is, then does that mean I really have not yet come to the point of being regenerated.

The desire to sin is still a very existent daily reality. I trust not in my own determination but I guess I can go to sleep every night, having repented, to know that his grace and mercy is more than sufficient to keep me from falling into apostasy the next day? It seems that my limited understanding of the reformed position seems to help my heart be in a better state of rest. Well lets see how the book shapes my understanding!

Here's the excerpt from the book where Marshall defines or comments on the perseverance of the saints.

From Page 22 of Btcl/Kept by the Power of God

On the one hand, the Christian life is a life which is continually sustained by the power of God. It does not merely depend upon a once-for-all gift of God received in the moment of conversion, but is a continual relationship to God in which His gracious gifts are received by faith. On the other hand, the believer is continually faced by temptations which jeopardize his faith. He is thus in a state of tension as he receives the gift of life from God and at the same time faces the forces of temptation which threaten to deprive him of that life. Positively, his duty is to grow in the Christian life towards the goal of sinlessness, i.e. of victory by the power of God over the temptations which assail him. This is the process known as sanctification. Negatively, the believer faces the danger of succumbing to temptation through failure to trust in God. He may be said to fall away from his faith in God, and the limit to this process would be apostasy, i.e. complete abandonment of faith and surrender to temptation; in such a case the divine life would cease to exist in the man.