In plain words
With your citta in Me, you will cross all difficulties by My grace. But if, from ahaṅkāra, you will not listen, you will perish.
Word for word
With mind on Me, you will cross all difficulties by My grace; but if from ahaṅkāra you will not listen, you will perish.
The commentators
Bhagavadgītābhāṣyam· bhāṣya
मच्चित्तः सर्वदुर्गाणि सर्वाणि दुस्तराणि संसारहेतुजातानि मत्प्रसादात् तरिष्यसि अतिक्रमिष्यसि । अथ चेत् यदि त्वं मदुक्तम् अहङ्कारात् ‘पण्डितः अहम्’ इति न श्रोष्यसि न ग्रहीष्यसि, ततः त्वं विनङ्क्ष्यसि विनाशं गमिष्यसि ॥ ५८ ॥
In plain words
Keep your mind on me, and every hard passage — all of them, the ones no one gets past on their own, thrown up by the very causes that keep saṃsāra turning — you will cross. You will walk straight past them, by my grace. But if ahaṅkāra speaks first, if you think *I already know this* and so do not listen to what I have said, do not take hold of it — then you are lost. You will go to ruin. || 58 ||
Close to the Sanskrit
With your mind on me, you will cross over — will step beyond — all hard passages, all of them impossible to cross, born of the causes of saṃsāra, by my grace. But if — that is, if you, out of egoism, thinking 'I am learned,' will not hear what I have said, will not take hold of it, then you will be lost, you will go to ruin. || 58 ||