What is a "Preacher of the Gospel"?

[Rakiura John]

In some 1813 Presbytery Minutes is an entry that "The Rev'd George Mark represented to the Presbytery that John Smith, Preacher of the Gospel, and Schoolmaster at Carnwath, had the prospect of leaving the County of the Presbytery and therefore wished for a Presbyterial Certificate ...".
 
Throughout the Presbytery Minutes the appellation "Rev'd" is applied when referencing a minister of religion, so in the above case there seems to be a clear distinction between a Reverend and a Preacher of the Gospel. What exactly is the latter?

[Skoosh]

A lay preacher John, there were such who travelled away to communion in distant parishes, often with outdoor preaching. (The Men!)

Skoosh.

[Forfarian]

I think, but I am willing to be corrected, that a preacher was a layman who preached and assisted the ordained minister. Sometimes you read about someone being 'licensed to preach by the Presbytery' who then goes on to be ordained and become a fully-fledged minister, so in some cases it was a step on the way to ordination, but not necessarily all preachers became ministers.

[Rakiura John]

Ah. I've just been looking at The Church of Scotland's Licencing of Probationers Act (an Act of the General Assembly) which includes a Presbytery having the ability "to Licence a person as preacher of the Gospel and probationer for the Holy Ministry". This Act is dated 1932 but it's likely something similar was around in the early nineteenth century. The fact John Smith was after a Presbyterial Certicate certainly suggests his preaching of the Gospel was somehow authorized or sanctioned by the Presbytery.

[Rakiura John]

And looking further at the current rules of the Presbyterian Church, a Presbytery can grant a Certificate for a Licentiate
7.10.1.Extract of minute of licence:
Mr ………………………………………………………, following his request and having forwarded all necessary certificates, was taken on trials for licence and has successfully completed all requirements. He satisfactorily answered the appointed questions put to him by the moderator and signed the formula. The presbytery licensed Mr …………………………………………… to preach the gospel of the Lord Jesus Christ.
Signed: (presbytery clerk)        Dated:

And it can grant a "Presbyterial Certificate" as follows:
7.10.2.Presbyterial Certificate:
At ………………… (place where meeting was held) and on ……………………… (date), by order of the presbytery of ……………………………………, it is certified that Mr …………………………… is a licentiate of this church, licensed by the presbytery of ………………………….. , and that his conduct is becoming of his profession.
Signed: (presbytery clerk)        Dated:

So for John Smith to ask for a Presbyterial Certificate indicates he did hold a Licence to Preach the Gospel.

[GR2]

It was very common, especially in the 17th and 18th centuries, for a minister to have started his career as a parish schoolmaster. Because the schoolmaster's salary was usually pretty low, it was normally the custom to employ him as session clerk (and sometimes also as precentor) to improve his income and attract a better quality of teacher to the parish.