What is the relation between our good works and salvation by grace? If we are saved by grace, then why bother with good works? This would seem to lead to a kind of lazy, powerless Christianity that doesn't result in any kind of change in a person's life. On the other hand, if salvation is by works, then we might fall into the trap of thinking that life in the kingdom is something we deserve.
Mark the Ascetic wrote a work included in the Philokalia called On Those who Think that They are Made Righteous by Works: 226 Texts. He addresses precisely this issue in the opening statements. His perspective is an important one and offers us a way ascetics in the more strenuous and difficult strands of Christianity considered this question.
He opens up with a categorical declaration of the nature of adoption as grace:
The Lord, wishing to show that every commandment is a duty, while, on the other hand, that adoption is given to men as a gift for the sake of His blood, says: "When you will have done everything commanded you, you say: 'We are worthless slaves and we have done just what we ought to have done.'" [Luke 17, 10] Therefore the Kingdom of heaven is not a payment for deeds, but the grace of the Master, prepared for faithful servants (2).
To be obedient is already your duty; you are supposed to do it anyway. Nevertheless Jesus rewards those who are obedient with the kingdom because he is gracious. He gives a gift that far outweighs the worthiness and value of the work it is "rewarding." Thus we are called to be obedient and we have no other option, but we should not think that we earn our way into the Kingdom through obedience. No, we are merely performing our duties. The Lord, on the other hand, is happy to give us a gift for being dutiful.
To show just how gracious this Lord is, Mark affirms: The one who wants to do a thing, but cannot, is considered by the one who knows the heart, God, as having done it. Yet this is to be understood as much with regard to good things, as also with regard to bad things (16). We know that adultery of the heart is as good as adultery. But Mark insists that God likewise sees and considers the desire for a good which cannot be realized. This notion is present in Isaac the Syrian, too.
Mark comes down heavy on those who are concerned only to have right faith without works, as well as those who are confident in their works:
Some, without obeying the commandments, reckon that they believe aright. Others, obeying them, expect the Kingdom as a payment owed to them. Both the ones and the others err with regard to the truth. The master does not owe his servants a payment; yet nevertheless, neither will those who do not serve aright inherit freedom (18-19).
This is a way of thinking about the relation of faith and works which, to my mind, makes a lot of sense. It fits the Biblical data very well. The judgment texts in the Bible (e.g., Mt 25; Rom 2) uniformly depict persons receiving entry into the kingdom as a reward for their works. It is something given to them because of what they have done, not what they believed or anything of the sort. At the same time it is clearly not a reward proportionate to the quality of their work done, since they have only done what they are supposed to do anyway, and are being given a gift far beyond that. This is the humbling grace of God: he gives us the Kingdom, which we could never merit, for doing only what we were supposed to do, anyway.
Such is the depth and gravity of our sin! That is how crappy human persons actually are -- that they have to be motivated to perform the bare minimum of their duties by a gift that no one could ever possibly have imagined or asked for themselves. But that is also how good God is -- that he doesn't throw us away when we are found incapable and unwilling even of doing what is necessary, let alone what is supererogatory. Instead he offers us a fantastic gift!
Mark offers the following (very provocative) advice:
When you hear the Scripture saying that God "will repay each according to his works" [Ps. 62.12], don't understand it as speaking of an equal proportionality with Gehenna or the Kingdom, but that Christ will repay the deeds of disbelief in Him or of belief -- not as a money changer who weighs the price of things to be exchanged, but as God, our Creator and Redeemer (22).