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एतत्समृद्धमत्यर्थं तपो भवति नान्यथा ॥ १२ ॥
In plain words
Practised this way, tapas ripens completely — richly, fully. Practised any other way, it does not. || 12 ||
Close to the Sanskrit
This tapas becomes exceedingly complete; not otherwise. || 12 ||