The power of dharana gets you to samyama which means, the union with the cosmic force of whose mantra you are chanting. This is how Sun gets his energy and helps the world. This is how five elements work. This is how all gurus work but it is all the DEGREE of their perfection they attain. Attaining perfection in it is a BLESSING in addition to karma you do on the earth and it has to be achieved through selfless karmic works. The karmic work also would vary based on their soul objectives. Every soul comes down with some objectives and  the purpose. By falling in that line of karma, one’s karma gets will be totally repaid by following this dharana (by which they attain samyama while doing that universal karma). So who becomes the doer of that universal karma? It is the cosmic source or the divine who is the doer of your mission. In doing your mission, as you cannot achieve it individually, the cosmic force joined you to achieve it and relieve you from your bondages. This is the background operation of the Guru in this path or in any other path.

 You can check this video to understand the power of Dharana Kriya.