Truthfulness is much more than the absence of lies. It is genuine communication of minds and hearts. Real truthfulness reflects the character of God, who is always exactly what He says He is, and who speaks painful but joyful truth, never any small talk to our hearts. Think of Jesus: ever kind, but relentlessly truthful.
O my God, in thee I trust, let me not be put to shame; let not my enemies exult over me. Yea, let none that wait for thee be put to shame; let them be ashamed who are wantonly treacherous.
The Revised Standard Version