Paul makes an interesting command concerning our attention:

Philippians 4:8–9 (ESV)

⁸ Finally, brothers, whatever is true, whatever is honorable, whatever is just, whatever is pure, whatever is lovely, whatever is commendable, if there is any excellence, if there is anything worthy of praise, think about these things. ⁹ What you have learned and received and heard and seen in me—practice these things, and the God of peace will be with you.

While not directly referencing this passage, William Spurtowe provided an illustration of the subjective effect of our attention. If we are not thinking on “these things” our attention will be the opposite direction. The effect that will be fear and depression:

Are not these genuine thoughts for a man to conceive that it is with him and with every Christian as it is with those who walk with their faces towards the sun, the dark shadow behind them; but when they turn from the sun, it forthwith changes its place comes before them. When they travel with their facts to the Sun of Righteousness, their paths are full of light and comfort; but when they turn from him, what dark images of death. What ghastly apparitions of hell and destruction go before them every step they tread. Yea, the further they wander from God, how does their terror increase, and their fears multiply, which are stretched out like the shadows of evening, until at length they be swallowed up in the black darkness of night?