Ishvara is the 5th Niyama. It means to surrender to your personal form of God, the divine, the universe or however you see it.
They say this is the most difficult for students to embrace, because it is not a process or a mindset.
It is the act of giving ourselves to a higher purpose.
This is why the sages guide us through the holy hymns to meditate because it is through meditation that we are able to have that relationship with the divine.