§ IFormulation
Since the cosmos is ordered by rational TERMprovidence, and everything that happens serves the good of the whole, the only rational attitude to one's own existence is gratitude. This is not politeness or bargaining (as in popular religiosity — "I give thanks in order to get more"), but the acknowledgement of a fact: I have received my being, my reason, and all the circumstances of my life. A complaint about what one has received has no ground; gratitude is not an affect but a correct categorisation. In Marcus, gratitude is tightly bound to acceptance of fate: the two are two modes of the single "yes" to what happens.
§ IISources in tradition
Cleanthes' Hymn to Zeus (SVF I 537) is the programmatic text of the Stoic attitude of gratitude. Epict. Disc. 1.16 (the whole of it "on providence" — "what else should I do but sing a hymn to god?"); Ench. 31; Disc. 1.6.19–22 ("if I were a nightingale, I would do what a nightingale does; I am rational — therefore I sing a hymn to god"). Sen. De ben. IV (the whole, on gratitude as a virtue). In Marcus: Med. 1 (the whole first book is an unfolded litany of thanks); 2.3; 5.31; 6.44; 9.40; 12.11.
§ IIINotes
In 02-03 this doctrine is the culmination: a life lived in the right teachings ends ἵλεως ἀληθῶς καὶ ἀπὸ καρδίας εὐχάριστος τοῖς θεοῖς — "truly serene and from the heart grateful to the gods" (see grateful-departure). Structurally, gratitude here functions as a criterion: that a person dies in gratitude is the sign that his philosophy is working. The alternative — γογγύζων ἀποθάνῃς, "to die murmuring" — is the diagnostic symptom that the teachings have not been interiorised.