In plain words
Therefore, best of Bharatas, first restrain the senses and cast off this sinful one that ruins both jñāna and vijñāna.
Word for word
Therefore you, having first controlled the senses, O best of the Bharatas, abandon this evil one, the destroyer of jñāna and vijñāna.
The commentators
Bhagavadgītābhāṣyam
यतः एवम् —
तस्मात् त्वम् इन्द्रियाणि आदौ पूर्वमेव नियम्य वशीकृत्य भरतर्षभ पाप्मानं पापाचारं कामं प्रजहिहि परित्यज एनं प्रकृतं वैरिणं ज्ञानविज्ञाननाशनं ज्ञानं शास्त्रतः आचार्यतश्च आत्मादीनाम् अवबोधः, विज्ञानं विशेषतः तदनुभवः, तयोः ज्ञानविज्ञानयोः श्रेयःप्राप्तिहेत्वोः नाशनं नाशकरं प्रजहिहि आत्मनः परित्यजेत्यर्थः ॥ ४१ ॥
In plain words
Since this is how it stands —
So you — first bringing your senses fully under your own control, Arjuna — must cast off this desire, this evil, wicked thing, this enemy we have been speaking of, the very thing that destroys both knowledge and discernment. Knowledge here means understanding the self and what belongs with it, learned from scripture and from a teacher. Discernment means actually living that understanding as your own experience. And desire destroys both of these — the very things that lead you to what is truly good. So cast it off — let go of it from within yourself. That is what is meant.
Close to the Sanskrit
Since (it is) thus —
Therefore you, having first restrained — mastered — the senses at the outset, O bull among the Bharatas, abandon — give up — this sinful, evil-conducted desire, this aforementioned enemy, the destroyer of knowledge and discernment: knowledge — comprehension of the self and the rest, from scripture and from the teacher; discernment — specifically, direct experience of that; the destroyer, the bringer of destruction, of those two, knowledge and discernment, which are the cause of attaining the highest good. 'Abandon' [means]: give up from yourself. This is the meaning.