The affix śatṛ comes after the verb arha in expressing praise.,
As अर्हन्निह भवान्विद्याम् 'thou art worthy of this knowledge here'; अर्हन्निह भवान्पूजाम् 'thou art worthy of honor in this place'.
Why do we say 'when meaning to praise' ? Witness अर्हति चौरो वधम् 'the thief deserves death'.,