SAMADHI means the fixing of the MIND.. free from all IMPULSES & AGITATIONS, on the LORD, or on one`s own REALITY..It indicates the state in which one is in one`s own REAL NATURE..
Samadhi is when one is FREE from all DUALITY..The mind will be UNSHAKEN by dual experiences..
It is UNMOVED / UNMOVABLE.. like having to thread a needle..have to be intent on the job and the end of the thread has to be kept straight & pointed..
SIMILARLY.. to enter the GRACE OF GOD, which is subtler than the subtlest, the mind has to be STEADY & the EYE and the SENSES have to be CONCENTRATED on the same process..