And in next verse Krishna says what happens to those who are faithless

Bg 3.32

ye tv etad abhyasūyanto
n
ānutiṣṭhanti me matam
sarva-jñ
āna-vimūḍhāṁs tān
viddhi na
ṣṭān acetasa

Word for word: 

ye — those; tu — however; etat — this; abhyasūyanta — out of envy; na — do not; anutiṣṭhanti — regularly perform; me — My; matam — injunction; sarva-āna — in all sorts of knowledge; vimūḍhān — perfectly befooled; tān — they are; viddhi — know it well; naṣṭān — all ruined; acetasa — without Kṛṣṇa consciousness.

Translation: 

But those who, out of envy, disregard these teachings and do not follow them regularly are to be considered bereft of all knowledge, befooled, and ruined in their endeavors for perfection.

ye tv etad abhyasūyanto, abhyasūyanto is envious so nānutiṣṭhanti, the previous verse was tisthanti which means to follow, those who do not follow my instructions. Abhyasūyanto, sarva-jñāna-vimūḍhāṁs tān
viddhi na
ṣṭān acetasa because of envey those who will not follow my instruction,

sarva-jñāna-vimūḍhāṁs tān, all their knowledge becomes deluded,

viddhi naṣṭān acetasa, cetasa means consciousness acetasa means misdirected consciousness SP translates with out Krishna Consciouness, and therefore all their endevour become ruined

So here what Krishna is telling, ultimately everything is meant to offer to Krishna and if we try to withdraw it to our own shallow, isolation and self-centered enjoyment then whatever knowledge we acquire whatever other endeavors all of those will be lost, why those will be lost because the soul without Krishna cannot be happy. Many of atheist philosopher of last century, by end of their life became mad and some committed suicide. An atheist philosopher has written that there is no God no soul and only this is the life we got which is full of sufferings so only question in life is whether to commit suicide tomorrow or today. It is gloomy and also not true.

sarva-jñāna-vimūḍhāṁs tān
viddhi na
ṣṭān acetasa

One who rejects Krishna will not achieve ultimate perfection, that person will stay in the bondage of material existence.

So in this way Krishna exhorts Arjuna to continue Karma Yoga and gradually rise to Bhakti Yoga.