Link to purport by A C Bhaktivedanta Swami Srila Prabhupada

Transcript of Bhakti-Shastri class on this verse by Chaitanya Charan

Bg 18.12

aniṣṭam iṣṭaṁ miśraṁ ca
tri-vidhaṁ karmaṇaḥ phalam
bhavaty atyāgināṁ pretya
na tu sannyāsināṁ kvacit

Synonyms: 

aniṣṭam — leading to hell; iṣṭam — leading to heaven; miśram — mixed; ca — and; tri–vidham — of three kinds; karmaṇaḥ — of work; phalam — the result; bhavati — comes; atyāginām — for those who are not renounced; pretya — after death; na — not; tu — but; sannyāsinām — for the renounced order; kvacit — at any time.

Translation: 

For one who is not renounced, the threefold fruits of action – desirable, undesirable and mixed – accrue after death. But those who are in the renounced order of life have no such result to suffer or enjoy.

Now Krishna is giving a broader perspective about the person who is attached, atyāgināṁ and one who is detached, sannyāsināṁ. 

The person who is atyāgi will get a result of aniṣṭam iṣṭaṁ miśraṁ ca, good karma good result ista, bad karma bad result anista, and there is misra, sometimes our actions are combination of good and bad 

aniṣṭam iṣṭaṁ miśraṁ ca
tri-vidhaṁ karmaṇaḥ phalam

These three kinds of fruits are there.

bhavaty atyāgināṁ pretya, pretya means after death this is also used earlier, the person who is not renounced  will get all these results in due course of time.
na tu sannyāsināṁ kvacit

but a sannyasi will not get these results. 

A Sannyasi will be free from these results and will eventually become liberated.

So previous verse the contradiction was between a person who is trying to give up all work v/s person who is acting with detachment. 

So person who is trying to give up all work is practically not possible. The person who is acting without attachment will become liberated. This is one comparison. Here both the persons are seeking liberation. But among these Krishna is saying the preferable is to act without attachment.

Now Krishna is doing a broad comparison between a person who is acting with attachment and a person who is working without attachment. So if we compare these two the person who is acting with attachment will lead to bondage, and person who is acting without attachment will lead to liberation.

End of transcription.