It is truly a great sin when much of men's most pleasing thoughts are spent on things that do not concern them. Thoughts are precious things, they are the immediate fruits and buds of an immortal nature. God has given us power to coin thoughts, lay them out in things that concern our own good, our own neighbor's good, and His own glory. And if we do not spend  them on these things, it is the greatest waste in the world.

Thoughts are the caterers for our lusts, they lay in all their provision.

It is the opinion of imagination that casts that varnish of goodness on sinful pleasures, for it is not truly in them. That the soul should, Ixion-like, embrace and commit adultery with clouds only, that is vanity beyond all vanities. This makes us more vain than any other creature, who though "subject to vanity," yet are not subject to such vanity as this.

When we defile our souls and spirits with these imaginations and likenesses which are conceived in our own fancies, being the children of our own hearts, it is worse than whoredom, it is incest!