”With all the energy we can put forth, we are but unprofitable servants.”
In Ultimatum from Either/Or Kierkegaard examines the common phrase “One does what one can” in relation to our service to God.
He concludes (in this section) that, while we wish to console ourselves (as we recognize ourselves to be unprofitable servants, perhaps) with the thought that we have done all we could, if we think about what we are saying or if we have ever striven to determine the bounds of what we can do to serve God, we remain in uncertainty, in anxiety. We are unprofitable servants.
And to the second half of this quote from MacDonald:
The way MacDonald expresses this passage sheds new-to-me light on it. In directing the young man to sell everything, give to the poor and “follow me” Jesus seems to be suggesting that the selling and giving were not the focus, neither was some eventual eternal reality, but that He himself was the fulfillment of the young man’s desire for eternal life. Sell everything, give the money to the poor (those who really need it and won’t be hindered by having some of it) was the way to move the man’s attention and pride from his stuff, so that he could redirect it toward the one he would follow and in whom he would find fulfillment.