It took several more days than I anticipated but here is a brief analysis of the second half of the Fifth Head of Doctrine from the Canons of Dort. Again this head of doctrine addresses the perseverance of the saints.
Article 8. 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.
Building on what they said before, the Synod affirms that perseverance of the saints is ultimately not the work of the saints, though they do work in it, but is the work of God. As a divine operation its success cannot be in doubt. God never fails in his endeavors. Left to our own strength and merit we would undoubtedly be lost yet according to the power and will of God as the merit of Christ is applied to our account we can never lose the gift of the Holy Spirit and the promise of eternal salvation.
Article 9. Concerning this preservation of those chosen to salvation and concerning the perseverance of true believers in faith, believers themselves can and do become assured in accordance with the measure of their faith, by which they firmly believe that they are and always will remain true and living members of the church, and that they have the forgiveness of sins and eternal life.
Therefore our assurance does not flow from looking to ourselves. As Calvin said, we when look at ourselves we only see damnable sin. Instead assurance of God's love is a saving grace that God gives to those he gives the gift of saving faith. So our confidence of belonging in the church and of eternal salvation is because we know that God who began a good work in us will be faithful to complete it.
Article 10. Accordingly, this assurance does not derive from some private revelation beyond or outside the Word, but from faith in the promises of God which he has very plentifully revealed in his Word for our comfort, from the testimony of the Holy Spirit testifying with our spirit that we are God's children and heirs (Rom. 8:16-17), and finally from a serious and holy pursuit of a clear conscience and of good works. And if God's chosen ones in this world did not have this well-founded comfort that the victory will be theirs and this reliable guarantee of eternal glory, they would be of all people most miserable.
Therefore we know that assurance of faith does not come from a private revelation that is given to us but is only found in the promise of God that are contained in Scripture and the Holy Spirit's work that makes the Word of God living and active in the people of God. So again we do not look to ourselves for assurance but we look to God's promises in his Word and then to the signs of saving faith described in that Word, particularly the internal testimony of the Holy Spirit and the external manifestation of the good works that we are created in Christ to do (Eph. 2:10).
Article 11. Meanwhile, Scripture testifies that believers have to contend in this life with various doubts of the flesh and that under severe temptation they do not always experience this full assurance of faith and certainty of perseverance. But God, the Father of all comfort, does not let them be tempted beyond what they can bear, but with the temptation he also provides a way out (1 Cor. 10:13), and by the Holy Spirit revives in them the assurance of their perseverance.
The Synod does not wish to discourage believers unbiblically and so they do state that even mature believers in this life will have to deal with doubts and will question their assurance in times of temptation. At the same time, the sure and certain promise in the Word is that God will not allow his elect to be tempted to the point where they would possibly fall away eternally but will renew them again to repentance and give them a new and greater certainty of faith.
Article 12. This assurance of perseverance, however, so far from making true believers proud and carnally self-assured, is rather the true root of humility, of childlike respect, of genuine godliness, of endurance in every conflict, of fervent prayers, of steadfastness in crossbearing and in confessing the truth, and of well-founded joy in God. Reflecting on this benefit provides an incentive to a serious and continual practice of thanksgiving and good works, as is evident from the testimonies of Scripture and the examples of the saints.
Because this assurance does not stem from ourselves but from God it does not serve as a source of boasting in ourselves or in our own work but rather causes us to humble ourselves and to rejoice in the Holy Spirit. It is ultimately as we reflect on the work of God in us to preserve us in our perseverance that we do persevere in good works to the glory of God.
Article 13. Neither does the renewed confidence of perseverance produce immorality or lack of concern for godliness in those put back on their feet after a fall, but it produces a much greater concern to observe carefully the ways of the Lord which he prepared in advance. They observe these ways in order that by walking in them they may maintain the assurance of their perseverance, lest, by their abuse of his fatherly goodness, the face of the gracious God (for the godly, looking upon his face is sweeter than life, but its withdrawal is more bitter than death) turn away from them again, with the result that they fall into greater anguish of spirit.
Here the Synod has careful words for those today who would try to use the doctrine of perseverance of the saints as an excuse for lawlessness (saying, "once saved, always saved"). This doctrine does not excuse sin and disobedience. Instead it places them in the proper context of a new relationship with God. The relationship is not one of wrath but now we are a part of the household of God. It behooves us as beloved children of God to live in a manner that is worthy of our calling and thus to seek to honor, please, and glorify our heavenly Father in our conduct and behavior.
Article 14. And, just as it has pleased God to begin this work of grace in us by the proclamation of the gospel, so he preserves, continues, and completes his work by the hearing and reading of the gospel, by meditation on it, by its exhortations, threats, and promises, and also by the use of the sacraments.
This grace of the perseverance of the saints is accomplished through the same means that the gospel is first delivered to us. It is through the means of grace, meaning the Word and sacraments, that the gospel promising eternal salvation to all who believe in Jesus Christ and repent of their sins is delivered to us.
Article 15. This teaching about the perseverance of true believers and saints, and about their assurance of it--a teaching which God has very richly revealed in his Word for the glory of his name and for the comfort of the godly and which he impresses on the hearts of believers--is something which the flesh does not understand, Satan hates, the world ridicules, the ignorant and the hypocrites abuse, and the spirits of error attack. The bride of Christ, on the other hand, has always loved this teaching very tenderly and defended it steadfastly as a priceless treasure; and God, against whom no plan can avail and no strength can prevail, will ensure that she will continue to do this. To this God alone, Father, Son, and Holy Spirit, be honor and glory forever. Amen.
The Synod closes in doxology. It is not believers but those outside who mock this doctrine. The church receives it as the gracious promise of the Bridegroom who died to purify her from all sins so that at the last day he might receive her unto himself in glory and thus rejoices and loves her Christ all the more while longing for that day.