In plain words
Their minds are in Me, their lives given to Me; enlightening one another and speaking of Me always, they are content and rejoice.
Word for word
With minds on Me, their prāṇas gone to Me, enlightening one another, and speaking of Me always, they are content and they rejoice.
The commentators
Bhagavadgītābhāṣyam
किञ्च —
मच्चित्ताः, मयि चित्तं येषां ते मच्चित्ताः, मद्गतप्राणाः मां गताः प्राप्ताः चक्षुरादयः प्राणाः येषां ते मद्गतप्राणाः, मयि उपसंहृतकरणाः इत्यर्थः । अथवा, मद्गतप्राणाः मद्गतजीवनाः इत्येतत् । बोधयन्तः अवगमयन्तः परस्परम् अन्योन्यम् , कथयन्तश्च ज्ञानबलवीर्यादिधर्मैः विशिष्टं माम् , तुष्यन्ति च परितोषम् उपयान्ति च रमन्ति च रतिं च प्राप्नुवन्ति प्रियसङ्गत्येव ॥ ९ ॥
In plain words
And further —
'Mind fixed on me' means simply this: those whose heart is set on me — that is what it means to have your mind in me. 'Life given over to me' means their very senses — sight and everything else — have come home into me, withdrawn completely into me. Or, said another way, it means their whole living has been given over to me. Talking with each other, helping each other understand, telling each other about me — my knowledge, my strength, my power, and every quality like these — they find themselves satisfied, they arrive at real contentment, and they delight, finding that very delight, just as one finds joy in the company of someone truly dear.
Close to the Sanskrit
And what further —
'My-minded': those whose mind is in me — they are 'my-minded.' 'My-gone-are-the-life-breaths': the vital faculties beginning with the eye, gone, attained, to me, of whom — they are 'my-gone-life-breaths,' that is, their organs withdrawn into me; this is the meaning. Or else, 'my-gone-life-breaths' means 'my-gone-is-their-very-living'; this is that. Instructing, causing to understand, each other, one another, and speaking of me as distinguished by qualities such as knowledge, strength, valor and so on — they are satisfied, they attain satisfaction, and they delight, and they attain delight — just as through the very company of someone dear.