आत्मानमन्तत उपसृत्य स्तुवीत कामं ध्यायन्नप्रमत्तोऽभ्याशो ह यदस्मै स कामः समृध्येत यत्कामः स्तुवीतेति यत्कामः स्तुवीतेति ॥ १.३.१२ ॥
In plain words
Finally, having drawn near to himself, let him sing praise, meditating upon his desire and not heedless; and swiftly indeed will that desire of his be fulfilled for which he sings praise — for which he sings praise.
The commentators
Chāndogyopaniṣadbhāṣyam· bhāṣya
आत्मानम् उद्गाता स्व रूप गोत्रनामादिभि — सामादीन् क्रमेण स्व च आत्मानम्— अन्तत अन्ते उपसृत्य स्तुवीत, काम ध्यायन् अप्रमत्त स्वरोष्मव्यञ्जनादिभ्य प्रमादमकुर्वन्। तत अभ्याश क्षिप्रमेव ह यत् यत्र अस्मै एवविदे स काम समृध्येत समृद्धिं गच्छेत् । कोऽसौ ? यत्काम य काम अस्य सोऽय यत्काम सन् स्तुवीतेति । द्विरुक्तिरादरार्था ॥
In plain words
Let the udgātā priest approach his own identity—his form, lineage, and name—and in proper sequence align the Samans with his own self. At the very conclusion, let him perform the chant with focused intent upon his desired fruit, remaining utterly vigilant over vowels, sibilants, and consonants without making a single slip. Thereupon, very quickly indeed, whatever desire this knower harbors will be fulfilled and reach complete prosperity. What desire is this? Whatever wish he holds when he undertakes the chant—being filled with that exact aspiration, he should chant. The repetition in the text is meant to show special reverence and emphasis.
Close to the Sanskrit
Let the udgata singer, having approached his own self by form, lineage, name, etc., and in due order the Samans and his own self, finally at the end praise, meditating on the desire, being vigilant with vowels, sibilants, consonants, etc., not making any mistake. Then very soon indeed whatever desire for this knower, that desire would prosper, would attain prosperity. Which one? Whatever desire—whoever has this desire of his, this one, being desirous of that, should praise, thus. The repetition is for the purpose of emphasis.