In the computer world, there is a saying that goes, "Garbage in, garbage out." The quality of the output that you get from a computer is in direct proportion to the quality of what you put into it. If you give the computer a set of nonsensical instructions, the resulting output will be nonsense. If your input is of a high quality, the output will also be high quality.
The same holds true for our hearts and minds. What we put into our hearts and fill our minds with will affect what flows from our hearts and minds. When we put "garbage" in, "garbage" comes out. We are living in an era in which we are bombarded with information. The internet, cell phones, computers and tablets, and, of course, television, all give us access to more information than ever before. While some of that information is good and even beneficial, there is also a lot of "garbage."
Scripture says that from the abundance of a man's heart his mouth speaks (Luke 6:45). If a man's heart is filled with that which is good, then his mouth will speak good. His life will reflect the good that has been put in his heart and mind. Conversely, if a man's heart is filled with things that are evil or immoral, things that are not good, then his mouth will speak evil. His life will reflect the evil that has been put into his heart and mind.
As children of God and followers of Christ, it is important that we fill our hearts and minds with things that will cause our lives to reflect God's goodness. God's Word has provided us with the solution to ensuring that what flows from our hearts and our lives does just that. In Philippians 4:8, Paul lists the kinds of things that we should think about, that we should focus our hearts and minds on - things that are true, noble, right, pure, lovely, and admirable. He then sums up these things, and all others like them, into two categories, anything that is excellent and praiseworthy.
When we fill our hearts and minds with things that are both excellent and praiseworthy, then what flows from our hearts and minds will also be excellent and praiseworthy. This is what God desires for us and it is what we should always strive for. Paul knew that these things were important to believers. His life and his words demonstrated his belief in our need to carefully monitor what we put into our hearts and minds. In Philippians 4:9, he tells us that, if we follow his example and "practice these things," then the peace of God will be with us.