Psalm 119,42 Then I can answer the scoffers, for I trust in your word.
This prayer is a close follow-up to what he asked for in the previous verse. There, David prayed that God's faithful love and his good salvation should come to him, as God had promised him. Now he tells God what he will do when he experiences God's mercy and works of grace.
Then he can answer the scoffers, because he trusted the word of God. In other words, he says that when he experiences answers to prayer, he can use this to show the scoffer that he is wrong. Once we have experienced that God has intervened in salvation, changing our lives, then it will close the mouth of the taunter. People may have many theories and thoughts about God, they may even deny that he exists, but our experience of God's faithful love and help can no one deny. We have experienced what we have experienced and no one can take that from us.
Nevertheless, we must understand that our experience does not stand alone. We have experienced salvation and God's good help because we trust in God's Word. This is important to point out. We believed the Word and acted upon it, then we experienced that it was true. Our experiences of grace and help come from faith in God's good promises. God has shown himself faithful. He has done as he said he would do. We have experienced that we can trust him and what he says.
In these days when the scoffers are speaking loudly, we must not be embarrassed by the word of God. When we trust in the Word of God, we will always have an answer to the scoffers. I believe the Bible is the word of God. I have confidence in what is written in the Bible. I believe the Law and the prophets. With this positive attitude to what God has said, it is quite easy to find good answers to questions or contradictions from people.
"I always want an answer to those who mock me, because I trust your words!"