He now started fashioning his masses based on fulfillment theology. Christmas eve celebrations of 1965 started with the reading of Hindu texts followed by the prophets and then Christian Gospel – thus Hindu texts becoming the preparation for the advent of Christianity. He called mantras as short prayer phrases which could be related to Christian devotion. In his work 'Prayer' he drew parallels between the Hindu Om and Sachhindananda and the Christian Abba, the prayer of Jesus. The mechanism for creating a Christian mantra, which Henri Le Saux called as 'Mantra Sandwich' was later consolidated in Shantivanam. Here a traditional Indic mantra venerated and practised for thousands of years like Om Nama Sivaya or Om Namo Bhagavathe Vasudevaya or Om Mani Padme Hung are taken. Then the Hindu or Buddhist spiritual principle (deity's name or symbol) is removed and Christian name is slipped in between.

Thus Om Nama Shivaya or Om Namo Narayana becomes Om Namo Christaya, Aum Sri Yesu Bhagavathe Namaha. Om Mani Padme Hung became Om Yesu Christa Hung. Ringu Tulku and Mullen in their paper 'Buddhist use of compassionate imagery' (2004) trace the Christian appropriation of Buddhist mantras to Shantivanam project and justify it through the fulfillment theology: "A strong connection between Om Mani Padme Hung, as a universal expression into human heart and the spirit of Jesus has already been made in Buddhist circles.”

In 1968, Henri Le Saux left Shantivanam handing over the charge to new occupants. On parting, he gave a four-fold advice to a Jesuit priest who had founded a Christian centre for dialogue with Hindus. In that advice, Henri Saux suggested that Christians should take up the celebration of Hindu festivals such as Deepavali as a joyful expression of their own faith and also use aarti or deepa puja in Christian churches giving it their own Christian interpretation.

There is an interesting twist in the life story of Henri Le Saux. Leaving Shantivanam and living by the banks of Ganges, there seemed to have happened in him some genuine transformation. According to Wayne Teasdale, a Catholic theologian, Henri Le Saux “seemed to lapse into purely monistic Advaita”. Abhishiktananda declared that it was the Advaitic experience and realisation that is important and everything else need to be dropped: