What does Hebrews 12:12 mean?

The writer continues using athletics as an analogy for spiritual growth. In prior verses, he mentioned that God's discipline was something to be expected from a good father, and especially from a heavenly Father (Hebrews 12:5–9). Discipline corrects us away from sin. It trains us to exhibit a deeper faith and to be more trusting of God. This chapter began with an encouragement: to "run the race" we're assigned by God (Hebrews 12:1). The prior verse mentioned how spiritual growth comes through "training," and used a Greek term specifically related to strenuous exercise.

Here, we see words which could easily be spoken to an athlete by his trainer. Spiritually, this passage encourages Christians to press on through hardships. Those experiences are certainly painful, at the time (Hebrews 12:11), but once we've been through them, we can see how God used those struggles to "train" us. Not only do these words serve as good athletic advice, and sound spiritual advice, they are also probably taken directly from the Old Testament. Isaiah 35:3 says almost the exact same thing, also in the context of encouragement and perseverance.