When the “seed of the spirit” starts to “grow in the human soul”

When a person becomes a Baha'i, actually what takes place is that the seed of the spirit starts to grow in the human soul. This seed must be watered by the outpourings of the Holy Spirit. These gifts of the spirit are received through prayer, meditation, study of the Holy Utterances and service to the Cause of God. The fact of the matter is that service in the Cause is like the plough which ploughs the physical soil when seeds are sown. It is necessary that the soil be ploughed up, so that it can be enriched, and thus cause a stronger growth of the seed. In exactly the same way the evolution of the spirit takes place through ploughing up the soil of the heart so that it is a constant reflection of the Holy Spirit. In this way the human spirit grows and develops by leaps and bounds.

Naturally there will be periods of distress and difficulty, and even severe tests; but if that person turns firmly toward the divine Manifestation, studies carefully His spiritual teachings and receives the blessings of the Holy Spirit, he will find that in reality these tests and difficulties have been the gifts of God to enable him to grow and develop." 
(From a letter written on behalf of the Guardian to an individual believer, October 6, 1954; compilation: Living the Life; compilation: Lights of Guidance)