4.42 Tasmat, therefore, O scion of the Bharata dynasty; atistha, take recourse to, i.e. undertake; yogam, yoga -performance of actions, which is a means to full Illumination; and now, uttistha, rise up for battle; chittva, cutting asunder; jnanasina, with the sword of Knowledge-Knowledge is full Illumination, which is a destroyer of such defects as sorrows, delusion, etc.; that itself is the sword; with that sword of Knowledge-;enam, this; samsayam, doubt; atmanah, of your own, which is a source of one's own ruin and is most sinful; hrtstham, in the heart, residing in the intellect; ajnana-sambhutam, arising from ignorance, born of non-discrimination.
The word atmanah is used because doubt concerns oneself. Indeed, another's doubt cannot be removed by someone else. Hence the word 'own' is used. So, although the doubt is with regard to the Self, it is really one's own.