A yogi is someone who practices yoga. Yoga means union, but union with what or who? When I think of a loved one it brings a smile to my face and I feel good inside. If that someone leaves me or becomes ill then thinking about them or having mental 'union' with them causes me sorrow. Human beings and situations always change so what brings delight at one moment can bring pain the next.
Brahma Kumaris meditation focuses on, or has union with a 'something' that doesn't change and that something is God. God is eternally lovefull, peaceful and blissful (in spite what you may have heard to the contrary), so thinking about God, having union with God in my mind brings peace and love to myself. God never changes. Everything else in this world does. God isn't of this world though He/She does visit it on occasions when we need help.
I used to think that God was unknowable but I was wrong. Using the concentrated power of my mind, learnt through meditation, I can connect, have union with God whenever and wherever I want.