[2] In 1949, Campbell felt called to rejoin the Faith Mission, which provided him with a house in Edinburgh.
The call came from the Reverend James Murray MacKay, at the prompting of two Gaelic-speaking sisters in their eighties, who had been praying for revival.
On one occasion Campbell was the main preacher at the Faith Mission Convention at Hamilton Road Presbyterian Church in Bangor, Northern Ireland, when he suddenly felt that he must leave at once, despite being engaged to speak at the closing meeting there the next day.
In 1958, Campbell was called to become principal of the Faith Mission's Training Home and Bible College in Edinburgh, where he served for a number of years, before retiring.
The first was that, in his view, a true revival was a move of God that affected, not only church members, but the surrounding community in a way that was visible to all parties concerned (work stopping, bars closing, crime ceasing, etc.).
His practice in evangelistic meetings was not to make the usual altar call, but to invite people to come to another room to pray and seek God.
In his own words, 'Seventy-five percent (of the people) were gloriously saved before they came near a meeting..... the power of God was moving!