It is indeed reasonable that we should do His will, for we are in this world only for that. Alas! Every day we ask Him that His will may be done; and when it comes to the doing, we have such difficulty! We offer ourselves to God so often; we say to Him at every step, "Lord, I am yours, here is my heart"; and when He wants to make use of us, we are so cowardly! How can we say we are His, if we are unwilling to accommodate our will to His?An excerpt from a letter by St. Francis de Sales (1567-1622) to a married woman. Emphasis mine.
Think of the nature of the commandments of God, which are mild, gracious, and sweet, not only the general commandments but also the particular ones of our vocation. And what is it, then, that makes them burdensome to you? Nothing, in truth, save your own will, which desires to reign in you at any cost....
We are not to choose at our own will. We must wish what God wishes; and if God wishes me to serve Him in one thing, I ought not to wish to serve Him in another.
Coming to that particular thing that troubles you, say, "Will You that I do such a thing? Ah! Lord, although I am not worthy to do it, I will do it most willingly," and thus you greatly humble yourself. Oh my God! What a treasure you will gain! One greater, without doubt, than you can imagine.