Being 'Upright' signifies truth that originates in charity. Truth may be derived from various origins, but the truth that has its origin in the good of charity from the Lord is called 'upright,' and 'an upright man,' as in Psalms 15:1-2, 18:25, and 84:11

(Reference: Arcana Coelestia 612; Psalms 84:11)