Ordination has existed since the earliest forms of the church as a way of distinguishing those who have particular unique callings from God to serve Christ in the church.In most denominations, only clergy–trained and authorized ministers of the Word and sacrament–are ordained. One of the most important hallmarks of a Presbyterian (USA) church, however, is the ordination of non-clergy to offices of church service. The PCUSA ordains clergy (teaching elders), elders (ruling elders) and deacons. Clergy and ruling elders serve coequally on the governing council of the church, called the Session. Deacons are called to ministries of care, service, and compassion. Trustees are not ordained, but manage many of the key business functions of the church.