Mom used to say, "If you don't have anything good to say, then don't say anything." Well, if you don't warn or notice the bad things then others may succumb to a deception or "pothole". However, there is some wisdom in that statement. Ephesians 4:29 admonishes the Christian - Do not let any unwholesome talk come out of your mouths, but only what is helpful for building others up according to their needs, that it may benefit those who listen. Paul continues a chapter later by stating - Nor should there be obscenity, foolish talk or coarse joking, which are out of place, but rather thanksgiving. (Ephesians 5:4) That is where I believe my mother was operating from - a clean speech policy - God Speak in the house and anywhere.
Isn't this "help" the sole reason Christians open up their mouths and share anyway? We have the best encouragement, hope, and answer for anyone. In his second letter to the church in Corinth Paul says, It is written: "I believed; therefore I have spoken." With that same spirit of faith we also believe and therefore speak, (2 Corinthians 4:13) And to the Romans Paul gets a little more specific - I will not venture to speak of anything except what Christ has accomplished through me in leading the Gentiles to obey God by what I have said and done-- (Romans 15:18) Paul magnifies the point that his words and actions have been nothing but Christ focused. In fact, this Christ centered speech and activity have God's seal of approval. Paul says to the church in Thessalonica - we speak as men approved by God to be entrusted with the gospel. We are not trying to please men but God, who tests our hearts. (1 Thessalonians 2:4)
It makes ALL the difference who you are speaking for and about. They [false prophets] are from the world and therefore speak from the viewpoint of the world, and the world listens to them. (1 John 4:5) With God's approval and entrusting of The Gospel, the perfect testing grounds for witnessing is simply talking about what God has done for you. Nobody can take that away. "We [Christians] have not received the spirit of the world but the Spirit who is from God, that we may understand what God has freely given us. This is what we speak, not in words taught us by human wisdom but in words taught by the Spirit, expressing spiritual truths in spiritual words. The man without the Spirit does not accept the things that come from the Spirit of God, for they are foolishness to him, and he cannot understand them, because they are spiritually discerned. The spiritual man makes judgments about all things, but he himself is not subject to any man's judgment: 'For who has known the mind of the Lord that he may instruct him?' But we have the mind of Christ." (1 Corinthians 2:12-16)
"Therefore each of you must put off falsehood and speak truthfully to his neighbor, for we are all members of one body. (Ephesians 4:25) Keep a clear conscience, so that those who speak maliciously against your good behavior in Christ may be ashamed of their slander. (1 Peter 3:16) Speak to one another with psalms, hymns and spiritual songs. Sing and make music in your heart to the Lord," (Ephesians 5:19)