In essence, contentment is wanting what God wants for us, and what He wants for us is Him. This is why the chief end of man is to glorify God and enjoy Him forever (WSC 1). We most glorify God when we most enjoy what He has created us to desire—Himself.
God has put eternity in our hearts. He has inscribed heaven on our souls. He created us to long for a perfect world and to desire what is supremely ideal. We want to be fully and finally free from the suffering and misery of this world, and ultimately from our sin—not only the conviction and sadness our sin brings us, but also the hurt and pain it brings to those closest to us. As redeemed but fallen creatures in this fallen world, we desperately want to be done with sin and its consequences. We want to be less proud, less impatient, less sad, less worried, less burdened, and we want to be more holy, more repentant, more prayerful, more at peace, and more content. We are, as Martin Luther taught, simul justus et peccator, “at the same time just and sinful.” In Christ, God has declared us righteous, though we still strive each day to mortify our sin in the flesh. But there is a day coming when we will no longer struggle, when our faith shall be sight, when we shall see Christ Jesus face-to-face, when we will no longer desire, no longer need, no longer lack contentment.