What if I came to you and told you that I had the whole book of Psalms memorized (yes, including chapter 119)?
If you had enough time, I would think that you would want me to "prove it." You would want me to show you that what I told you is true.
It is possible that I would have the whole book memorized, but it's very possible that it could be "fake news." (And by the way, I would love to have that much memorized, but I am not even close to it.)
In life you will be told many different ideas and philosophies. Some of them may be true, but some of them will be false. How can you know and decide what is true and what is false?
1 Thessalonians 5:21 Prove all things; hold fast that which is good.
If you were to go out and pan for gold, you will realize very quickly that you cannot just grab a handful of earth and pick out the gold pieces. You need to sift the earth in a pan to separate the valuable from the worthless.
In this world we must be careful. There is a lot out there that is worthless and harmful. We must remember that only God's Word is the truth and of value.
A mind not sifted in the Word of God is a mind that is willing to go along with what the world says is truth...
...and that path has led many young teens down a path away from God.
Paul is reminding us in 1 Thessalonians 5:21 to prove all things, or sift all things. Only cling to the valuable, the truth. The more you sift your mind in the Word of God, the more you will prove all things, see the good and hold on to it.
So, have you spent some time in God's Word today? It is incredibly hard to prove all things when you aren't running to the Bible!