Canons of Dort Head 5 Article 3

By reason of these remains of indwelling sin, and the temptations of sin and of the world, those who are converted could not persevere in a state of grace if left to their own strength. But God is faithful, who having conferred grace, mercifully confirms and powerfully preserves them therein, even to the end.

Canons of Dort—Head 5—Article 9

Of this preservation of the elect to salvation and of their perseverance in the faith, true believers for themselves may and do obtain assurance according to the measure of their faith, whereby they arrive at the certain persuasion that they ever will continue true and living members of the church; and that they experience forgiveness of sins, and will at last inherit eternal life.