VERY day that we live, we should fill it up with good things. If we don't fill it up with good things, the devil will certainly make sure that it is filled up with other things. Notice some of the good things that Paul promotes here: rejoicing (vs. 4), moderation (vs. 5), & prayer (vs. 6). Then he starts painting with just as broad of a brush as he can, as he writes, "Whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good report; if there be any virtue, and if there be any praise, think on these things" (vs. 8). That just about covers it, doesn't it? Intentionally, we must fill our minds with good thoughts. On purpose, I must do the good things that I know to do (vs. 9). With careful planning, you must allow Christ to conquer evil in your own life by His grace, and His grace in action works through the principle of replacement (Daniel 4:27, 1st Corinthians 13:11 & Romans 13:12).
Now, we can't always change our circumstances. Paul had things come upon him that were not so good, but there were things he did have control over (even in very bad situations). He had learned to focus on good things, even in bad times (vs. 11-13). Not that he had figured this out on his own. He had the help of Christ in taking on this new and better perspective. He understood the generosity and power of the Spirit (vs. 19). He was willingly submissive to the objective of giving God glory. He was dependent upon God's grace. And so, through faith in God, Paul had learned that when someone brings us lemons, we are to make lemonade. We should carefully and deliberately look for the good in every condition. If Romans 8:28 tells us that all things work together for the good of those who love God, then we might as well look for good from the beginning.