"12Wherefore lift up the hands which hang down, and the feeble knees; 13And make straight paths for your feet, lest that which is lame be turned out of the way; but let it rather be healed." (Hebrews 12: 12-13)
In the previous verses of Hebrews chapter 12, the writer is exhorting his Hebrew Christian brethren to accept the discipline of walking by faith, looking not just to the example of Old Testament saints who believed but never saw the Messiah come, but to Jesus Himself, our High Priest forever, whom we do not see, but we rest in the truth of knowing that He has accomplished all things for us.
Like the early Christians, today believers have a hard time believing that the work has been fulfilled, and like sulking children who want things done their way, they still hanker after the old habits, the only means.
Consider the constant complaining of the Israelites when they fled Egypt:
"11And they said unto Moses, Because there were no graves in Egypt, hast thou taken us away to die in the wilderness? wherefore hast thou dealt thus with us, to carry us forth out of Egypt? 12Is not this the word that we did tell thee in Egypt, saying, Let us alone, that we may serve the Egyptians? For it had been better for us to serve the Egyptians, than that we should die in the wilderness." (Exodus 14: 11-12)
Whenever the children of Israel faced trials of faith, immediately they wanted to go back.
Moses would exhort them:
"13And Moses said unto the people, Fear ye not, stand still, and see the salvation of the LORD, which he will shew to you to day: for the Egyptians whom ye have seen to day, ye shall see them again no more for ever. 14The LORD shall fight for you, and ye shall hold your peace." (Exodus 14:13-14)
So, when we read in the verses of Hebrews to strengthen our hands and knees, we are invited to stop feeling sorry for ourselves, to stop dragging our feat, demanding that God take away our problems. Instead, let us ask to see more of Jesus, that the eyes of our full understanding would see who Jesus is, how much He loves us, and what He is doing for us (Ephesians 3: 16-19).
Rather than resisting the grace of God, and trusting our own efforts, let us permit the Spirit of God to inform us of who Jesus is, and let us be transformed to be more like Him (2 Corinthians 3: 18; 1 John 3: 1-3). The chastening to be more like Him will not please our flesh, but we should not seek to gratify that dead part of ourselves, because we are alive in Him (Colossians 3: 1-4).