Link to purport by A C Bhaktivedanta Swami Srila Prabhupada

Transcript of Bhakti-Shastri class on this verse by Chaitanya

Bg 18.78

yatra yogeśvaraḥ kṛṣṇo
yatra pārtho dhanur-dharaḥ
tatra śrīr vijayo bhūtir
dhruvā nītir matir mama

Synonyms: 

yatra — where; yoga–īśvaraḥ — the master of mysticism; kṛṣṇaḥ — Lord Kṛṣṇa; yatra — where; pārthaḥ — the son of Pṛthā; dhanuḥ–dharaḥ — the carrier of the bow and arrow; tatra — there; śrīḥ — opulence; vijayaḥ — victory; bhūtiḥ — exceptional power; dhruvā — certain; nītiḥ — morality; matiḥ mama — my opinion.

Translation: 

Wherever there is Kṛṣṇa, the master of all mystics, and wherever there is Arjuna, the supreme archer, there will also certainly be opulence, victory, extraordinary power, and morality. That is my opinion.

yatra yogeśvaraḥ kṛṣṇo, wherever there is Krishna who is yogeśvaraḥ, master of all mystic power, 

yatra pārtho dhanur-dharaḥ, Arjuna has raised his bow

at the end of first chapter Arjuna has put aside his bow and arrow and now he has picked up his bow and arrow, which means Arjuna is ready to follow Krishna’s instruction ready to do Krishna’s will.

Arjuna’s bow and arrow represents living entity’s determination to serve Krishna. 

In the beginning of BG Arjuna used Pratakshya and Anuman by which his determination to serve Krishna was lost, but after Sabda his determination becomes strong. Similarly when we see around we may lose interest in Bhakti but after hearing and contemplating we can again get faith in Bhakti. So hearing regularly is very important in Bhakti. 

tatra śrīr vijayo bhūtir
dhruvā nītir matir mama

So wherever there is Krishna (The Lord) and Arjuna (determined devotees) there will be śrīr, opulence, Jaya, Vijaya, bhūtir is extraordinary power like Bhuviti is used in 10th chapter of BG. Nītir, morality also. 

This is also answer to Dhritarastras’s 1st question, what happened. Immediately what happened is BG was narrated, but the implication of Dhritarastras’s question was who won, so Sanjaya is making a prophesy that where there is Arjuna and Krishna there will be victory and opulence. 

So although powerful warriors are on the side of Kauravas but since Krishna is on the side of Pandavas, goddess of victory and opulence Shri will be where Her Lord will be there. So there will be bhūtir, the extraordinary power of Krishna. 

Krishna taught Shato Shatyam lesson and also the morality towards Supreme Lord and morality towards spirituality is the supreme morality.

Srila Prabhupada Purport: the last instruction of the Gītā is the last word in all morality and religion: surrender unto Kṛṣṇa.

…

By proper use of that independence he comes under the direct order of Kṛṣṇa. Thus he attains his normal condition in the pleasure-giving potency.

End of transcription.