As a part of its spiritual philosophy, Mustard Seed Communities has established St Thomas House. It is a community of men and women seeking a life of commitment as Laypeople, Priests, Brothers, and Sisters whose mandate is to initiate and promote all aspects of the spiritual well being of the organization. Through their daily diverse activities within the various ministries, these committed individuals are the custodians of the cornerstone of Mustard Seed Communities.

By virtue of the fact the Mustard Seed Communities is a Roman Catholic organization, the fundamentals of the Church form part of the basis upon which the spirituality of the organization is established. Among other devotions, there are the customary practices of Mass, Holy Rosary and Morning Office. All the residents at Mustard Seed Communities are encouraged to be baptized and to participate in the relevant sacraments of the Church. However, no one is excluded nor alienated as a result of their religious beliefs or affiliations. In fact all the religious functions (as far as possible) have embraced the wider community in an ecumenical spirit.

The members of St Thomas House are involved in all aspects and at all levels of the Mustard Seed Communities. They live as a community (men apart from women) and abide by the tenets that generally cover Catholic religious community life, and accept the counsels of poverty, chastity and obedience. They are encouraged to familiarize themselves with the local culture and to be in tune with the mood of the people, to enable them to impact more meaningfully in the execution of their apostolic work.

The community member is expected to fulfil certain criteria: a willingness to serve, a generous spirit and a strong commitment to the mission and purpose of Mustard Seed. S/he is expected to possess the ability and maturity to function independently and be self-motivated. The nature of the organization demands that all the committed members must be capable of balancing their apostolic, academic, social and physical development, under their own instigation.

Mustard Seed Communities will accept candidates from practically anywhere in the world. S/he will first go through a period where there is no obligation to long-term commitment; then, if suitable, makes a pledge for a particular time, where s/he will be of service to the organization. Thereafter, should any one consider themselves called to religious life, the necessary training will commence. Ultimately, St. Thomas House is a team of persons giving themselves as missionaries in the forefront of the Mustard Seed ministries, regardless of where it may lead. They form an integral part of Mustard Seed Communities, giving spiritual nourishment, and showing, by example, a life of fulfilment founded in the teachings of our Lord, Jesus Christ.