The doctrine of eternal punishment is often a hard pill for believers to swallow. On the one hand we understand the necessity of the doctrine; but on the other hand, it rubs up against our human sensibilities. Wayne Grudem in his excellent Systematic Theology lays out this struggle well:

What are we to think of this doctrine? It is hard – and it should be hard . . . If our hearts are never moved with deep sorrow when we contemplate this doctrine, then there is a serious deficiency in our spiritual and emotional sensibilities.

The reason it is hard for us to think of the doctrine of hell is because God has put in our hearts a portion of his own love for people created in his image, even his love for sinners who rebel against him. As long as we are in this life , and as long as we see and think about others who need to hear the gospel and trust in Christ for salvation, it should cause us great distress and agony of spirit to think about eternal punishment. Yet we must also realize that whatever God in his wisdom has ordained and taught in Scripture is right. Therefore we must be careful that we do not hate this doctrine or rebel against it, but rather we should seek, insofar as we are able, to come to the point where we acknowledge that eternal punishment is good and right, because in God there is no unrighteousness at all. (Grudem, Systematic Theology, 1151-1152)

May God grant us the grace to think rightly and lovingly about the hard doctrines of eternal punishment and hell.