In plain words
Mentally surrendering all actions to Me, taking Me as supreme and relying on buddhi-yoga, keep your citta constantly in Me.
Word for word
Having laid down with the mind all actions in Me, with Me as the highest, having resorted to buddhi-yoga, be constantly with mind on Me.
The commentators
Bhagavadgītābhāṣyam
यस्मात् एवम् —
चेतसा विवेकबुद्ध्या सर्वकर्माणि दृष्टादृष्टार्थानि मयि ईश्वरे संन्यस्य ‘यत् करोषि यदश्नासि’(भ. गी. ९ । २७) इति उक्तन्यायेन, मत्परः अहं वासुदेवः परो यस्य तव सः त्वं मत्परः सन् मय्यर्पितसर्वात्मभावः बुद्धियोगं समाहितबुद्धित्वं बुद्धियोगः तं बुद्धियोगम् अपाश्रित्य अपाश्रयः अनन्यशरणत्वं मच्चित्तः मय्येव चित्तं यस्य तव सः त्वं मच्चित्तः सततं सर्वदा भव ॥ ५७ ॥
In plain words
Because this is how it stands —
With a mind made clear by discernment, hand over every action to Me — every act with a visible aim and every act with an unseen one — the way you were already told: 'whatever you do, whatever you eat, offer it to Me' (Gītā 9.27). Let Me, Vāsudeva, be the one supreme goal of your life; give your whole sense of self over to Me. Take your stand in the discipline of a settled, gathered mind — no other refuge but that. Keep your attention fixed on Me and Me alone. Not sometimes — always. This is what I'm asking of you: be that.
Close to the Sanskrit
Since thus —
With the mind — with the discriminating intellect — having renounced in Me, the Lord, all actions having seen and unseen aims, by the principle already stated 'whatever you do, whatever you eat' (Bhagavad Gītā 9.27): 'having Me as the supreme' — I, Vāsudeva, am the supreme of whom, of you; you, being one whose entire self has been offered up to Me, having Me as the supreme; having taken recourse to the discipline of the intellect — the state of having a composed intellect, the discipline of the intellect, having taken recourse to that discipline of the intellect — recourse, meaning the state of having no other refuge; 'one whose mind is on Me' — mind of whom, is on Me alone, of you; you, one whose mind is on Me, constantly — always — be! || 57 ||