Kubera's last life on earth was about 7,500 years ago during Dvapara Yuga when the human lifespan was about 1,000 years. In this life he was a powerful asura, actually the chief of all asuras. During this life of hatred for Lord Vishnu, as sometimes happens, that hatred suddenly flipped to love. This is similar to what happens at the end of Kali Yuga when ignorance and hatred are at their maximum, and then suddenly the times change to Satya Yuga where all is Bliss, love and devotion to God. Kubera's change of heart required that he leave the ranks of the asuras and become a sura and serve Lord Vishnu.
To purify his life from all the negative karma brought about from the asuric activity, he performed yajñas to all the Grahas and was granted freedom from his karma and attained Brahman Consciousness. He accepted the jiva Avatara Incarnation of Krishna during the final years of his life on earth to exhibit the Unlimited Wealth Quality of Bhavagan. This jiva Avatara Incarnation of Krishna transformed his disfigured and dwarf-like physiology into the beautiful qualities of his Absolute Body, which is how he appears today in the Celestial Realms.
Lord Brahma was so delighted to welcome Kubera into His Celestial Family, that he ordered Vishwakarma, the architect of the devas, to build Kubera a chariot. Vishwakarma conceived and built Pushpak, an aerial chariot that moves of its own accord and which is so large that it can contain a whole city. Kubera would fly in this fantastic chariot and throw down jewels and other precious objects to people on the ground to help them materially so they could devote their time to God Realization.
When Kubera left his physical body at the end of his last life on earth, he joined the ranks of the Ascended Masters and was given the task to financially help all those on earth who desire Krishna Realization so they could have a comfortable life and achieve their objective.
With the full cooperation of Mahalakshmî, who exists in Her Absolute Body in Goloka, and through Her Expansion into this universe as Lakshmî, a yajña was created to connect devotees of Krishna in this universe with Kubera so that the wealth he holds for them could flow into their lives. The extent of the wealth that flows in the life is governed by the karma of the individual. Those who have performed all 12 of the Graha Yajñas will receive 100% of the benefit of wealth. Others will receive a reduced benefit due to negative wealth karma that is still active in their lives. However, any devotee of Krishna who performs this yajña sincerely and with devotion can receive sufficient wealth so they are financially self-sufficient and can devote their lives to Realizing Krishna.
In the picture below, we see Mahalakshmi. The Divine Light around Her head also indicates She is a Divine Absolute Being, and around Her are many stars, symbolic of Goloka. She is showering wealth in the form of gold coins into our universe for distribution by Kubera and his shaktis (called kinnaris). His wife and principal shakti, Kauberi is pictured at his left side.