Spentomard Gatha ... the third of the 5 Gathas
As I understand, Asho Zarathustra explains centrality of 'Righteousness' and its criticality for happiness through-out the body of this Gatha.
Righteousness is Central to Zoroastrianism. It is about being in right standing with God and the virtues prescribed by his teachings. Self- Righteousness on the other hand is about giving the final onus for one's decisions not to God but to ones own self and judgment.
Righteousness - being right, is the central theme. Through “Righteousness” which is the best among all the good virtues, good thoughts are produced in the mind. From good thoughts, best speech evolves and induced by best speech, pure actions are triggered & delivered.
Thus by the Grace of Dadar- Ahura-Mazda & through befriending “Spenta-Mino” (the one who supports progresses in evolution), we mortals are able to bring happiness from both the worlds ... the Corporeal world & the Spiritual world.
This Gatha urges men to observe righteousness for spiritual and early happiness.