The Bible compares the Christian life to a race:

Do you not know that those who run in a race all run, but only one receives the prize? Run in such a way that you may win. (1 Corinthians 9:24)

...holding fast the word of life, so that in the day of Christ I will have reason to glory because I did not run in vain nor toil in vain. (Philippians 2:16)

I press on toward the goal for the prize of the upward call of God in Christ Jesus. (Philippians 3:14)

Therefore, since we have so great a cloud of witnesses surrounding us, let us also lay aside every encumbrance and the sin which so easily entangles us, and let us run with endurance the race that is set before us... (Hebrews 12:1)

I have fought the good fight, I have finished the course, I have kept the faith (2 Timothy 4:7)

Thirty years ago I read a book by Steve Farrarr called Finishing Strong (Amazon link). The premise of the book, if I recall correctly, was that many people start out their Christian life full of gratitude and zeal and willing to do anything for Jesus. But over time, temptations and compromises come our way. We may stumble, stray, or slowly lose our steam. Some wipe out, some crash and burn. What matters is not how we start the race, but how we finish it. You may stumble and struggle and grow weary (I know I do!), but the faithful Christian who earns the reward in heaven is the one who keeps going. When he wipes out he gets back up and keeps pushing forward. He stays faithful to the end. 

It's been thirty years since I read the book. I don't remember any specifics but I remember finding it insightful and encouraging. As I've continued on in my Christian life, that long-haul vision has stuck with me all these years. Following Jesus, staying faithful, is not easy. It can be a slog at times carrying His light and love through a dark world, daily wrestling with sin both around us and within us. 

But if you have that mindset, it makes it easier to push on.

Maybe this cartoon will help encourage someone else who is huffing and puffing and wanting to quit. Keep going. Stay faithful.