The verse 22 in this hymn deals with the division of people into groups based on different vocations like rulers, rājanya, scholars and advisers brāhmaņa, the expert with the arrow etc; The division is based on the principle varņa, which is derived from vrn, to describe. The division of society, popularly called as caste, was based on varņa, i.e., according to their occupation, and not according to the color as certain orientalists have thought. Many of the brāhmins of south India are of a very dark complexion. RV (1.113.6) and RV (8.35.16-18) specifically deals with the four-fold division.
The verse 18.48 quoted prays on behalf of all the four groups for their enlightenment.
By your light, (ruchā), give Light or Knowledge to us Brahmins;
give Light to the kings;
give Light to the Vaishya and Light to the Shūdra;
give me also the Light or Knowledge. SYV (18.48)
Rucham: Light or Knowledge.
May brāhmaņās, possessing the lustre of spiritual knowledge be born,
and may there be born in this State
the man capable of ruling the people (rājanya),
the hero, expert with the arrow, an excellent marksman, and a great warrior;
And may there be cows giving plentiful milk,
the good draught-bull, and the swift horse.
May there be the woman at home with husband and children.
May there be born to the worshipper
heroic youths with the will to victory, the best
of chariot-fighters, fit to shine in assemblies.
May parjanya shower rains according to our needs;
may our trees, bearing fruit, ripen,
may our exertion and rest prosper. (22.22)