This can be particularly seen in Sri Rudram.
नमो - बभ्लुशाय विव्याधिनेऽन्नानां पतये - नमः
नमो - भवस्य हेत्यै जगतां पतये - नमः
नमो - रुद्रायाततायिने क्षेत्राणां पतये - नमः
नमः - सूतायाहन्त्याय वनानां पतये - नमः
There is Namaskara both at the beginning and end.
Why is this so?
Rudra has got both aspects: protective and destructive.
He protects everything.
But when pralaya comes he has to destroy the world he has protected thus far.
Considering this dual character of Rudra, he is offered Namaskara twice:
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Glory of Venkatesha
Story of Sri Yantra
Sages and Saints