In plain words
How much more then brahmins of holy birth and royal sages who are devoted to Me. Having come into this impermanent and joyless world, worship Me.
Word for word
How much more then holy brāhmaṇas, devoted, and likewise royal sages; having come into this impermanent, joyless world, worship Me.
The commentators
Bhagavadgītābhāṣyam· bhāṣya
किं पुनः ब्राह्मणाः पुण्याः पुण्ययोनयः भक्ताः राजर्षयः तथा । राजानश्च ते ऋषयश्च राजर्षयः । यतः एवम् , अतः अनित्यं क्षणभङ्गुरम् असुखं च सुखवर्जितम् इमं लोकं मनुष्यलोकं प्राप्य पुरुषार्थसाधनं दुर्लभं मनुष्यत्वं लब्ध्वा भजस्व सेवस्व माम् ॥ ३३ ॥
In plain words
And if even the wicked can reach this, how much more the virtuous brahmins, born into merit, already devoted — and the royal sages besides? A rājarṣi is simply one who is both king and sage together. So, given all of this, here is what follows: having reached this impermanent world — fragile as a single moment, and without any real happiness in it — this human birth, so rare, so hard to attain, and the one true opportunity for reaching what life is actually for — worship Me. Serve Me. Don't let this chance slip by.
Close to the Sanskrit
How much more, then, [do] virtuous brahmins, [that is,] of virtuous origin, [who are] devotees, and likewise royal sages [attain]? Rājarṣi [means]: they [who are both] kings and sages [are] rājarṣis. Since this is so, therefore, having obtained this impermanent, [that is,] fragile as a moment, and unhappy, [that is,] devoid of happiness, world, [namely] the world of human beings, [which is] the means for [attaining] the goals of human life, [and] difficult to obtain, [namely] having attained human-hood, worship, [that is,] serve, Me.