I Thess. 2:13 And we will never stop thanking God that when we preached his message to you, you didn't think of the words we spoke as being just our own. You accepted what we said as the very word of God--which, of course, it was. And this word continues to work in you who believe.
It is not always easy to know the truthfulness of what someone is saying these days. There are some very good speakers who can be very convincing who do not speak the truth. Many speak their own ideas and sometimes they clash with the truth. How can we know for sure that what we hear and believe is true?
We must be good students of God's Word ourselves. We cannot rely on what others tell us it means and believe it. We must examine the Word and think it through ourselves. When we do, we must bathe it in prayer with an open mind and heart. We must stay close to God so that we can be certain it's the Holy Spirit who is guiding our thoughts as we study the Word.
If we still do not quite understand what is being said, we turn to reliable sources for answers. We seek out the counsel of people who we know are mature in the faith and have a good grasp of the Scriptures. We also can find insight from what others have written in commentaries and books. It is important that we do our research until we have reasonable cause to believe what we believe God is saying is true.
A good test as to whether or not something is indeed true is that it works. God's Word works. It can be seen at work in others and experienced in ourselves. It stands the test of time. It never fails to do what it claims to do. If what you believe just doesn't seem to work out in life, then be assured it's not from God.