Diksha translated as a “preparation or consecration for a religious ceremony”, is giving of a mantra or an initiation by the guru (in Guru–shishya tradition) of Indian Culture. The word is derived from the Sanskrit root dā (“to give”) plus kṣi (“to destroy”) or alternately from the verb root dīkṣ (“to consecrate”). When the mind of the guru and the disciple become one, then we say that the disciple has been initiated by the guru. (Info. Credit Wikipedia)
From ancient times Diksha is an important ritual of Indian Culture. It is believed that only after Diksha ceremony, a person gets a rebirth (without physical death). It is mentioned in Atri Smrati that a human is born without any knowledge and only after Diksha Ceremony he get transformed and eligible for new birth and gets inner knowledge.
After getting Diksha from a living Sadguru, disciple life gets magical transformation. Sadguru initiates transfer and locking of higher energies into disciple Heart, Third eye and Crown Chakra during process of Diksha through mediums like Mantra, Divyaastra and Devastra.
As disciple progresses in his/her spiritual journey through regular meditation, the seed given by Sadguru gets transformed into a full blown tree having beautiful flowers and disciple gets experiences of Samadhi. By faithful devotion, association and selfless service towards Sadguru, disciple gets transformed into similar energy as Sadguru and gets fruitful results of Samadhi. Disciple negative energy gets converted to positive energies through these Divyaastra and Devastra given by Sadguru.
With the accumulation of this energy, disciple Kundalini gets erupted and travels through all his Chakras, leaving disciple in an state of supreme peace. This supreme peace, which cannot be achieved through different mantras, yoga and other rituals, can be easily obtained with just a blessing (Diksha) from living Sadguru. Once disciple gets Diksha, his actual spiritual journey gets initiated. He keeps on living a righteous way of life with gradual steps towards liberation.