That is one of the hallmarks of Presbyterian belief - the perseverance of the saints, one of the five points of Calvinism. No doctrine of the Christian faith can bring more joy or comfort to the heart of the believer than this one. The doctrine declares that once God has begun the work of redemption in any person, He will persevere in this work to the end and He will not let one of His own be lost. Yet, we also read here in this passage and elsewhere in the epistle and the New Testament the call to perseverance. The doctrine of the final perseverance of the saints has as its corollary the teaching that the saints are the people who persevere to the end.
Continuance is the test of reality in the Christian faith.
They were the ones Jesus said received the Word with joy, but soon thereafter when persecution and tribulation came their way, they gave up the faith. This is precisely what the author to the Hebrews feared for his readers, and it is for that reason that he urges them to hold on to their faith with courage and hope. It is persevering faith that holds onto Christ with boldness and rejoices in certain hope of better things to come. True Christian confidence is unwavering faith in a trustworthy God, and He who has promised to keep us is eternally faithful. He will be with us no matter what we may be called to go through.