The soul’s “progress and success, in all the worlds of God” is dependent on the virtue of ”truthfulness”

Truthfulness is the foundation of all human virtues. Without truthfulness progress and success, in all the worlds of God, are impossible for any soul. When this holy attribute is established in man, all the divine qualities will also be acquired. 
(‘Abdu’l-Baha, quoted by Shoghi Effendi, ‘The Advent of Divine Justice’)