Like the initial run of a half-hearted athlete slows down to a mere walk in a long marathon, so the circumstances of life and personal thoughts of discouragement often dull the prompting of the Spirit to continue steadfastly until the race of life is over.
These circumstantial and internal pressures have ensnared many people, who by stopping short of true faith, have missed eternal life altogether.
Take for example Judas. His impatience for the glory of a kingdom and his love for money slowed down his following of Christ till it stopped altogether and turned into a vengeful pursuit instead. His treacherous end evidenced the absence of faith in Christ. His initial love for Christ had quickly faded into a total betrayal of Christ.
Another person that lacked the endurance that comes from true faith was Demas. In the letters of Colossians and Philemon we meet Demas as a fellow-worker of the Apostle Paul. He was a man who like Judas initially fell in love with Christ and His teaching. But he lacked endurance. In 2 Timothy 4:10 we read of how, in the marathon of faith, Demas had glanced side-ways one too many times and quit the race because the side-lines of this world seemed more inviting that did Christ.
In 1 Timothy 1:19-20 a man with the name of Hymenaeus had made shipwreck of his faith. What made him give up and turn away from Christ? According to 2 Timothy 2:16-18, bad theology and sensational half-truths were the traps that caught Hymenaeus and his friends.
Selfishness and greed, worldliness and bad theology were the poisons that killed endurance in the lives of Judas, Demas and Hymenaeus. They never made it to Heaven.
Take stock of your own faith. Do your own pursuits in life dull your pursuit of Christ, His grace and commandments, or will you endure by looking to Christ in all things (Hebrews 12:1-3)?