Charles H. Spurgeon on Psalms 119:113

Vain thoughts. Our thoughts are set upon trifles and frivolous things, neither tending to our own profit nor the benefit of others: "The heart of the wicked is little worth; "all their debates, conceits, musings, are of no value: for all their thoughts are taken up about childish vanity and foolish conceits. "The thought of foolishness is sin" (Proverbs 24:9); not only the thought of wickedness, but foolishness. Thoughts are the firstborn of the soul, the immediate issues of the mind; yet we lavish them away upon every trifle. Follow men all the day long, and take account of their thoughts. Oh! what madness and folly are in all the musings they are conscious of: "The Lord knoweth the thoughts of man, that they are vanity" (Psalms 94:11). If we did judge as God judges, all the thoughts, reasonings, discourses of the mind, if they were set down in a table, we might write at the bottom, Here is the sum and total account of all, nothing but vanity.

The sins that do most usually engross and take up our thoughts are,

First. Uncleanness. Speculative wickedness makes way for active: "Hath committed adultery...in his heart" (Matthew 5:28). There is a polluting ourselves by our thoughts, and this sin usually works that way.

Secondly. Revenge. Liquors are soured when long kept; so, when we dwell upon discontents, they turn to revenge. Purposes of revenge are most sweet and pleasant to carnal nature: "Frowardness is in his heart, he deviseth mischief continually" (Proverbs 6:14), that is to say, he is full of revengeful and spiteful thoughts.

Thirdly. Envy. It is a sin that feeds upon the mind. Those songs of the women, that Saul had slain his thousands, but David his ten thousands, they ran in Saul's mind, therefore he hated David (1 Samuel 18:9). Envy is an evil disease that dwelleth in the heart, and betrays itself mostly in thoughts.

Fourthly. Pride. Either pride in the desires or pride in the mind, either vain glory or self conceit; this is entertaining our hearts with whispers of vanity: therefore it is said, "He hath scattered the proud in the imagination of their hearts" (Luke 1:51): proud men are full of imaginations.

Fifthly. Covetousness, which is nothing but vain musings and exercises of the heart: "A heart they have exercised with covetous practices" (2 Peter 2:14). And it withdraws the heart in the very time of God's worship: "Their heart goeth after their covetousness" (Ezekiel 33:31).

Sixthly. Distrust is another thing which usually takes up our thoughts distracting motions against God's providence. Thomas Manton.