"Therefore lift your drooping hands and strengthen your weak knees, and make straight paths for your feet, so that what is lame may not be put out of joint, but rather be healed" (vs. 12-13)
Hebrews 12 encourages us to willingly accept God's discipline. Discipline is a rather heavy word; as the author of Hebrews also writes: "Discipline always seems painful rather than pleasant..." (vs. 11) As Christians, we have incorporated this word into our term for "spiritual disciplines," those activities we do to strengthen our faith. Classically, the spiritual disciplines include things like praying, reading the scriptures, fasting, giving, serving, etc.
Chapter 12 goes on to tell us how important it is that we endure and profit from discipline, rather than reject or turn from it. Citing three Old Testament figures (Esau, Moses, and Abel), the author once again illustrates the superiority of the Christian faith and the necessity of turning away from evil.
To be fair, we should finish the quotation of Hebrews 12:11: "Discipline always seems painful rather than pleasant at the time, but later it yields the peaceful fruit of righteousness to those who have been trained by it." Be a long-term thinker when it comes to accepting the Lord's discipline. It will help you to firm up your flabby faith!