Charles H. Spurgeon on Psalms 119:113

I hate vain thoughts, A godly man may have roving thoughts in duty. Sad experience proves this; the thoughts will be dancing up and down in prayer. The saints are called stars; but many times in duty they are wandering stars. The heart is like quicksilver which will not fix. It is hard to tie two good thoughts together; we cannot lock our hearts so close, but that distracting thoughts, like wind, will get in. Hierom complains of himself; "Sometimes, "saith he, "when I am about God's service, I am walking in the galleries, or casting up accounts." But these wandering thoughts are not allowed: "I hate vain thoughts, "they come as unwelcome guests, which are no sooner spied, but turned out of doors. Thomas Watson.