Christ says this to help us rein in attitude, and to think soberly about ourselves. This is key to the defeat of pride. Pride so easily attaches to what we do, not just in the world, but in the spiritual realm also. Satan is quick to flatter us, and to get others to flatter us, and to tell us how great we are, how successful we are, what gifts we have, how we compare with others, what knowledge we have, how pleased our Master should be with us. Everything we do right is used as a weapon against us to throw us off balance. How can we cast off all this self-praise? By reminding ourselves that all we have done is through the grace of God at work within us. But also by remembering our many, many shortcomings and failures. Have we done anything that has actually added to the Lord God in any way? Have we brought profit to God in the sense that we have done something that he could not have done without us? Certainly not. We are his servants, but our service is given to us not for his benefit, but for ours. It costs him much to make us his servants, and he has to train us to do this service constantly. He has to put up with repeated failures to listen to his instruction, to do our work in the right spirit, to be consistent in our service, and to not let it go to our heads. Even when we have carried out our tasks as carefully as we can, there is still sin mixed with it. We must undermine our own pride by not forgetting this, and thank the Lord for the opportunity to serve him. We have done no more than our duty, and a master has the right to expect his servant to carry out all his duty without any great fuss being made of him.
Wonderfully, the Lord will reward his servants, and he does reward them even now. But the full reward will not come until it is safe for us to receive it. Not until the flesh, the sinful nature, has been removed from us, by death or by translation, can we safely receive this great reward.