Ps. 19:14 May the words of my mouth and the thoughts of my heart be pleasing to you, O LORD, my rock and redeemer.
What we say matters a lot. Words have the power to heal or destroy. They can either make or break someone's spirit. They can either lead someone to faith or lead them away from faith. We must take what we say seriously. In order for our words to be pleasing to God, our hearts must be right with Him. We speak what is in our hearts. If we let our heart go to pot, the things we say will not be good. We cannot neglect our souls and expect our words to be pleasing to God, even when we say good things.
What we think about matters. We have a very hard time controlling our thought lives. Many of the things that flow through our heads we don't want anyone else to know about, but God knows. We dwell on many things that we should not dwell on. We have thoughts about others that we shouldn't have. It's a good thing we don't verbalize all the things we think about. In order for us to please God in our thought lives, we must exercise self-control. We can't always prevent our thoughts from developing, but we choose whether or not we will dwell on them. The more we dwell on those things which are holy and good, the less of a hold unholy and bad thoughts will have on us.
When God is our Lord, He is our rock and redeemer. He gives us the power and means to please Him. God can be pleased with us with what we say and think about things. When Jesus is our rock, we will not fall into the cesspool of sin. He redeems us and sets us free from sin's hold on us. He takes all of our sinful deeds, words and thoughts and washes them away by His shed blood on Calvary. It is when we let our focus on Christ wander that we begin to have trouble.