We may struggle from time to time with unbelief. This is different from doubt, which likely most or all of us have on occasion. The father of a boy experiencing convulsions had unbelief.
Is the Old Testament important to us, as New Testament Christians, attending New Testament churches? What does the Old Testament have to do with us?
The words we speak have an impact on those who hear us speak. Because of this fact the Apostle Paul encourages us to speak with grace.