In plain words
When your buddhi, confused by differing scriptural statements, becomes steady and unmoving in the self, then you will attain yoga.
Word for word
When your buddhi, confused by what it has heard, stands unmoving, steady in samādhi [the self], then you will attain yoga.
The commentators
Bhagavadgītābhāṣyam
मोहकलिलात्ययद्वारेण लब्धात्मविवेकजप्रज्ञः कदा कर्मयोगजं फलं परमार्थयोगमवाप्स्यामीति चेत् , तत् शृणु —
श्रुतिविप्रतिपन्ना अनेकसाध्यसाधनसम्बन्धप्रकाशनश्रुतिभिः श्रवणैः प्रवृत्तिनिवृत्तिलक्षणैः विप्रतिपन्ना नानाप्रतिपन्ना विक्षिप्ता सती ते तव बुद्धिः यदि यस्मिन् काले स्थास्यति स्थिरीभूता भविष्यति निश्चला विक्षेपचलनवर्जिता सती समाधौ, समाधीयते चित्तमस्मिन्निति समाधिः आत्मा, तस्मिन् आत्मनि इत्येतत् । अचला तत्रापि विकल्पवर्जिता इत्येतत् । बुद्धिः अन्तःकरणम् । तदा तस्मिन्काले योगम् अवाप्स्यसि विवेकप्रज्ञां समाधिं प्राप्स्यसि ॥ ५३ ॥
In plain words
Suppose you ask: "The thicket of delusion has been crossed, and through that doorway the wisdom born of discriminating the Self has come to me — so when do I reach what karma-yoga bears as its fruit, standing in the highest reality itself?" Then listen.
'Pulled about by scripture' means: confused, tugged in different directions by the many scriptural passages that lay out ends and means, some urging action, some urging its opposite. But when your understanding finally stands still, becomes steady, unmoving, free of that scattering and wavering, it will be 'in samādhi' — and samādhi simply means the place where the mind becomes composed, which is the Self itself. So 'in samādhi' really means 'in the Self.' 'Unmoving' means the same thing again: free of any wavering between one view and another. Here, 'understanding' just means the mind. At that point, you will attain yoga — you will attain discriminative wisdom, real concentration.
Close to the Sanskrit
If [the question is]: "When shall I, having gained the wisdom born of discrimination of the Self by way of the crossing beyond the thicket of delusion, attain the fruit born of karma-yoga — the yoga of the highest reality?" — then hear that.
'Confused by scripture' — being confused, understood in various ways, distracted by the many scriptural texts revealing the connections of means and ends, characterized by engagement and disengagement — when your understanding, [at whatever time,] will stand, will become fixed, will be unmoving, devoid of distraction and wavering, [it will be] 'in samādhi' — 'that in which the mind becomes composed' is samādhi, [that is,] the Self; 'in that,' 'in the Self' — this is what is meant. 'Unmoving' — in that regard too, devoid of vacillation — this is what is meant. 'Understanding' [here means] the mind. Then, at that time, you will attain yoga — you will attain discriminative wisdom, concentration. [End of commentary on verse 53.]