Concentration can be explored as a function of mind, as an essential and distinct part of the path of liberation and as a "felt experience" in this very moment. Each exploration deepens understanding and empowers concentration.
Deepening concentration moves on two axis - horizontal and vertical. Continuity, or staying over time, is the horizontal axis. Intimacy, or the movement toward dissolving the subject/object, is the vertical axis. Together concentration deepens.
The practice of samadhi requires commitment to wise effort towards concentration. it requires overcoming resistance to concentration, to be willing to feel intimacy with teh object. The fruit of commitment to concentration is one-pointed equanimity. Concentration can be considered om five different qualities from dedication to steadiness.
To deepen our meditation practice we need to work skillfully with whatever is a disturbance -- whether it's the gross forms of the hindrances, or the subtlest manifestations of restlessness. This subtle restlessness often comes from a primal anxiety. We need to recognize this and find the stillness in our experience. Then we can truly be with things as they are.