ये शास्त्रविधिमुत्सृज्य यजन्ते श्रद्धयाऽन्विताः। तेषां निष्ठा तु का कृष्ण सत्त्वमाहो रजस्तमः ॥

ye śhāstra-vidhim utsṛijya yajante śhraddhayānvitāḥ teṣhāṁ niṣhṭhā tu kā kṛiṣhṇa sattvam āho rajas tamaḥ

Those that sacrifice full of faith, but casting aside the ordinances of the Scriptures, what is verily their condition, O Krishna? Is it one of Purity, Passion, or Darkness?

In plain words: Arjuna asks Krishna: what about people who worship with real faith but don't follow the rules of scripture? Is their faith pure, passionate, or dark?