Sutra:
82. iththAl virOthiyaik kazhikkiRathu.
83. virOthi thAn mUnRu.
84. athAvathu - SvarUpa virOthiyum, upAya virOthiyum, prApya virOthiyum.

Meaning:
82. With the namaS, obstacles are removed.
83. There are three obstacles.
84. They are, SvarUpa virodhi, upAya virodhi and prApya virodhi.

Sri PBA Swami's Sarartha Deepikai:
The namaS removes obstacles which are of three type. They are SvarUpa virodhi, upAya virodhi and prApya virodhi.

The SvarUpam was gathered out of the praNavam and the obstacle to that is SvarUpa virodhi. The means is born out of the meaning of namaS and the obstacle to that is upAya virodhi. The goal is described by the nArAyaNAya and the obstacle to that is upEya virodhi.

It was shown before that the Thirumantra explains the SvarUpam, upAyam and purushArttham. Since all three have virodhis, the namaS removes those obstacles.

The SvarUpam which is sEshatvam has the ahankAra mamakAra obstacles. The upAyam which is looking to no one but Him has the obstacle which is the belief that the self can be protected by itself. The purushArttham which is service to Him has the obstacle that the jIva derives pleasure for itself in that service.

How does the namaS remove these obstacles?

As told by Sri Parasara Bhattar in Ashtasloki "mantrabrahmaNi madhyamEna namasA pumsa: svarUpam gati: gamyam shikshitamikshitEna purata: pashcAdapi sthAnata:", the namaS joins with the parts before and after (kAkAkshi nyAyam)and also stays by itself, and removes the three virodhis. Joining with the part before, it becomes "Om nama:"; joining with the part after, it becomes "nArAyaNAya nama:"; by itself it becomes "namO nama:".