As a frontier city, well guarded inside and out, so protect yourselves. Do not let the right moment pass; those who miss the moment grieve in hell.

Nagaraṁ yathā paccantaṁ — like a frontier city (paccanta). The city on the border is vulnerable: exposed to constant attack, it must always be vigilant. The mind is that frontier city, besieged by desires and distractions.

Khaṇo vo mā upaccagā — do not let the moment (khaṇa) pass you by (upaccagā). The right moment for practice is fleeting. Whoever misses it later finds themselves in suffering (niraya), lamenting what they did not do.

The image of the fortified city resonates with yoga: saṁvara (sense restraint) is the inner wall that protects the mind. Without it, the forces of attachment enter without resistance.