4.40
अज्ञश्चाश्रद्दधानश्च संशयात्मा विनश्यति | नायं लोकोऽस्ति न परो न सुखं संशयात्मनः ||४०||
ajñaśh chāśhraddadhānaśh cha saṁśhayātmā vinaśhyati nāyaṁ loko'sti na paro na sukhaṁ saṁśhayātmanaḥ
Translation
But ignorant and faithless persons who doubt the revealed scriptures do not attain God consciousness; they fall down. For the doubting soul there is happiness neither in this world nor in the next.
Interpretation
The opposite of the qualified student: the ignorant, the faithless, and the doubter ('saṁśhayātmā' — the doubting soul) perish. The doubting soul has no happiness — neither in this world (where doubt prevents committed action) nor in the next. Doubt, when not used productively as inquiry but as chronic indecision, is a spiritual poison.