The Canons of Dordrecht
The Fifth Main Point of Doctrine: The Perseverance of the Saints
Article 8: The Certainty of This Preservation
So it is not by their own merits or strength but by God’s undeserved mercy that they neither forfeit faith and grace totally nor remain in their downfalls to the end and are lost. With respect to themselves this not only easily could happen, but also undoubtedly would happen; but with respect to God it cannot possibly happen, since his plan cannot be changed, his promise cannot fail, the calling according to his purpose cannot be revoked, the merit of Christ as well as his interceding and preserving cannot be nullified, and the sealing of the Holy Spirit can neither be invalidated nor wiped out.