Thompson wrote the following in the 1820s many years before he changed his views and became a Hardshell anti means adherent. What he says here is the old Baptist position. (emphasis mine)
"Wherein Sarah and her son were a figures of the gospel and those under it, first she was a figure of the gospel in her name Sarah, which signifies lady, princess, princess of the multitude; and this name was given to her because the blessing of God was upon her, and nations of people should of her, to denote that the gospel was to go amongst all nations, with the blessing of God attending it, and bring forth children in different nations, who are to be born again of an incorruptable seed by the word of God, which by the gospel is preached unto you."–
Again, Sarah was Abraham’s companion and ruler in his house, to shew that the gospel was a companion of God, and a rule in his house, whose house ye are. –
Again, Sarah lived in Abraham’s affections, long before she brought forth any children; so thegospel is the good will of God towards his people; which lived in his affections long before it was manifest in bringing forth children to him. –
Again there was a set time for Sarah to bring forth Isaac, so there was a set time for the gospel dispensation to take place. Sarah brought forth a promised seed, to denote that the gospel brings forth a seed of promise, or the heirs according to promise. -
Again, Sarah's son was born after Agar's to denote that the gospel dispensation should be after the law, and as Sarah was a figure of the gospel, or its dispensation, so her son was a figure of those under it; or the spiritual seed of Abraham, first in his name Isaac, which signifies laughter, and may denote the joy and gladness experienced by all those born under the ministration of the gospel. Isaac was not born after the flesh, but after the spirit, to denote that those born under the gospel, are born not of the flesh but of the spirit. Isaac was Abraham’s heir to denote that those born under the influence of the gospel, are heirs of God and joint heirs with Christ. Isaac was born by promise, to denote that those born under the gospel, as Isaac was, are the children of the promise. And as Isaac was persecuted by Ishmael, so it is now: but as then Agar and her son were cast out, and Ishmael could not be hear with Isaac; so the glory of the law disappears, and those under it are cast out, when the superior glory of the gospel breaks forth amongst the Gentiles, and brings forth its heaven born children; and so we see that these things are an allegory, for these are the two covenants." (See Chapter 56 - On Conviction III)
Children are begotten by the Gospel. That was the position of Thompson before the rise of the Hardshells.