You brood of vipers! How can you speak good, when you are evil? For out of the abundance of the heart the mouth speaks. (Matthew 12:34 ESV)
It matters what we say, because what we say reflects what we think, what we feel, what we understand, what we truly believe and confess. It what we say publicly to people, about them, what we conclude. Because in our words and thoughts and feelings are the buds from which will flower and bear our fruit.
Good fruit or bad fruit. A tree is known by the fruit it bears.
So what we say matters. What we think matters. What we feel matters. What’s in our heart matters. Because from all this spring our deeds, and the deeds that matter, as Matthew notes, are simple ones, acts of kindness and mercy and in a cruel and merciless world — food for the hungry, a cup of water to the thirsty, clothing to the naked, and company for the sick, lonely, and imprisoned.
It is hard to work deeds of love and mercy when your heart is cruel and unkind. The heart will out. Thoughts and feelings will out.
Jesus says our words and our deeds will be measured. We will be judged on the basis of what we say and do.
So our words matter.