Chapter VI Sloka 18

yda ivinyt< icÄmaTmNyevavitóte,
in>Sp&h> svRkame_yae yuKt #TyuCyte tda.

yad˜ viniyataÕ cittam
˜tmanyev˜vatiÿ÷hate |
ni×sp®ha× sarvak˜mebhyo 
yukta ityucyate tad˜ ( 6|18)||

When the perfectly controlled mind rests in the Self only, free from longing for all the objects of desires, then it is said, 'He is united'.

Commentary: Perfectly controlled mind: The mind with one-pointedness.
When all desires for the objects of pleasure seen or unseen die, the mind becomes very peaceful and rests steadily in the Supreme Self within. As the Yogi is perfectly harmonised, as he has attained to oneness with the Self and as he has become identical with Brahman, sense phenomena and bodily affections do not disturb him. He is conscious of his immortal, imperishable and invincible nature.

Yukta means 'united' (with the Self) or harmonised or balanced. Without union with the Self, neither harmony nor balance nor Samadhi is possible. (Cf. V. 23; VI. 8)