Commonly, the phrase "where two or three are gathered in my name, there am I in the midst" (Matt. l8:20) is applied to small gatherings for worship or prayer. It does bear this application but the original context shows that Christ is speaking of a Church Court. It is important to not that this is not the irreducible minimum for a congregation, rather it is the irreducible minimum for church government and discipline. This is evident because Christ speaks of two or three agreeing together as a church court on earth regarding anything they would request, it would be done for them by His Father in heaven. "For where two or three [plural] are gathered together in My Name, there am I in the midst them [plural]."
Two or three is an important principle in Church Government and order as shared between the Old and New Testaments. This is the case in terms of the minimum number of witnesses (Matt. 18:15-16; Deuteronomy 17:6 and 19:15). In the case of prophets participating it is a maximum number (1 Cor. 14:27&29). In Matthew 18 the two or three refer to the elders gathered to judge the case (Deut. 19:17), they have a ministerial, delegated binding and loosing authority (v. 18). Therefore Samuel Rutherford says, referring to the size of a church court, that "two or three faithful ones in the Church of the Jews, no less than in the Christian Church were a true visible church, having the power of the keys". It is true that as George Gillespie notes, it is "a dictate of reason, to ask counsel of a greater number when the counsel of a few cannot resolve us, then reason, being ever like itself, will dictate so much to a congregation, that they ought to submit to the authority of a greater number when their own authority is not sufficient to end a controversy among them." Yet this is only where matters are unresolved. Noone can question or decline the authority of a church court on the basis of the number of its members.
As Rutherford puts it elsewhere, the size of a church court does not relate to its authority, "the authority of Synods consisting of six onely, differeth not in nature and essence, from a generall councell of the whole Catholike visible Church" (Due Right of Presbyteries, p.331). "Synods should take care that no man despise their Authority". On 20 December, 1560, the first General Assembly of the Church of Scotland convened in Edinburgh, under the leadership of John Knox. Six ministers and 36 elders gathered to deliberate on and eventually to present for the approval of the Scottish Parliament the Book of Discipline. It was a small court for the nation but had all due authority.
There was a proposal after the time of the Scottish Reformation to have small Presbyteries — comprising "ane or twa," [one or two] "thrie or four" kirks — but this was never carried out. In 1581 the General Assembly considered a "forme how elderschips may be constitute of a certain number of parochines lyand together,"
and in this form all the parishes in Scotland were grouped under fifty Presbyteries,
"twenty to every Presbytery, or thereabouts." This form was modified but was the basis of the structure. Two or three is the quorum, however, for a presbytery. Three members of Presbytery form a quorum, two of them being ordained ministers.
Another significant number is 7, as in Acts 6. It is said that in many Patristic Churches there were approximately seven Congregations associated in each Presbytery., and then again seven such Presbyteries associated together in one Regional Synod (Dr FN Lee). Perhaps this was drawn from the seven churches of Asia. Although the Presbytery of Antioch had five Preaching Elders (Acts 13:1).
A small presbytery enables greater familiarity but it can also present challenges in providing assessors and dealing with matters of discipline and other difficult areas. The point is that size is not related to authority. As the Reformer Martin Bucer said; "the number of parishes in which such as meeting is convened is an extraneous circumstance, pertinent in no respect to the essence of the particular church"