Bhagavad Gita: Chapter 8, Verse 27

नैते सृती पार्थ जानन्योगी मुह्यति कश्चन |
तस्मात्सर्वेषु कालेषु योगयुक्तो भवार्जुन || 27||

naite sṛitī pārtha jānan yogī muhyati kaśhchana
tasmāt sarveṣhu kāleṣhu yoga-yukto bhavārjuna

nanever; etethese two; sṛitīpaths; pārthaArjun, the son of Pritha; jānanknowing; yogīa yogi; muhyatibewildered; kaśhchanaany; tasmāttherefore; sarveṣhu kāleṣhualways; yoga-yuktaḥsituated in Yog; bhavabe; arjunaArjun


BG 8.27: Yogis who know the secret of these two paths, O Parth, are never bewildered. Therefore, at all times be situated in Yog (union with God).


Yogis are aspirants who are striving to unite their minds with God.  Knowing themselves to be tiny fragments of God, and the futility of a lascivious life, they attach importance to the enhancement of their love for God, rather than the temporary perceptions of sense pleasures.  Thus, they are the followers of the path of light.  Persons who are deluded by the Maya, thinking of this temporary world as permanent, of their body as the self, and of the miseries of the world as sources of pleasure, follow the path of darkness.  The results of both paths are diametrically opposite, one leading to eternal beatitude and the other leading to the continued misery of material existence.  Shree Krishna urges Arjun to discriminate between these paths, and become a yogi, thereby following the path of light. 

He adds a phrase there, “at all times,” which is very important.  Many of us follow the path of light for some time, but then regress to the path of darkness.  If someone wishes to go northward, but keeps going four miles south for every mile north, then that person will end up being south of the starting point, despite endeavoring greatly.  Similarly, following the path of light for some time in the day does not ensure our progress.  We must constantly move ahead in the right direction and stop moving in the wrong direction, only then will we go forward.  Hence, Shree Krishna says, “Be a yogi at all times.”