John Trapp on Isaiah 66:9

Ver. 9. Shall I bring to the birth, and not cauſe to bring forth?] i. e. Shall I ſet upon a work and not go through with it? God began and finiſhed his work of Creation: Chriſt is both Authour and finiſher of his peoples faith, Heb. 12.2. The holy Ghoſt will ſanctifie the Elect wholly, and keep them blameleſſe unto the coming of our Lord Jeſus Chriſt, 1 Theſ. 5.23. Neſcit tarda molimina Spiritus ſancti gratia, ſaith Ambroſe: Otherwiſe his power and mercy would not equally appear to his people in regeneration, as the power and mercy of the Father and the Son in Creation and Redemption.