Certain critics of Christianity consider it a slight to declare our faith as merely a “crutch” for the weak. They might be surprised to know that I agree: it is a crutch, but that's no critique! Just as Jesus turned the Cross from a symbol of shame to an emblem of power, so I relish the reality of leaning on Him who hung there for me. (And as for weakness: 2 Corinthians 12:9 calls me to lean on the all-sufficient grace of the Lord, for His strength is made perfect in my weakness.) Reading Jeremiah 33:14-18 inspires me to rely all the more on Jesus as the Branch who is not only the fruitful Vine in whom we grow, but also the faithful Rod on whom we lean. People who dismiss Christianity as a shameful crutch for the weak tend to rely upon their own strength, to prize their own wisdom—yet fail to see their own need.
Of course, we ALL struggle with the daily temptation to "lean on our own understanding" (see Prov 3:5) while relying upon the rationale, intellect, and power of the visible world and the things it esteems. In 2 Kings 18:21 & Isaiah 36:6 the same words in both passages describe this kind of carnal thinking & worldly reliance, specifically addressing how God's people at the time were looking to the political superpower of Egypt to guide and provide for them:
“Look, I know you are depending on Egypt, that splintered reed of a staff, which pierces the hand of anyone who leans on it! Such is Pharaoh king of Egypt to all who depend on him.”
God had already long prior shown His supremacy not only over Pharaoh but indeed over ALL the gods of Egypt, and He had done so through the humble staff in the hands of His servants Moses & Aaron (see e.g. Exodus 4:2-5; 7:8-10; 8:5; 14:16). There’s a sermon in this, of course! Those who rely upon worldly powers and turn to worldly strength find that worldly strength breaks under their weight and pierces their hand. (I remember bleeding profusely on a couple of occasions as a kid when having this happen with some walking sticks on hikes—ouch!)
Something different happens, though, when we trust in the Lord with all our hearts and lean not on our own understanding: He straightens our paths and guides our steps (Proverbs 3:5-6). Truly, Jesus is the Branch we can lean on, the staff that doesn’t disappoint and even heals (compare Numbers 21:8 & John 3:14-15). He doesn’t splinter under pressure and pierce our hands, but rather He was the tender shoot out of dry ground broken for us (Isaiah 53). He took upon Himself the piercing that was due to us (Psalm 22:16; Zechariah 12:10; John 19:37; Revelation 1:7) and gave us instead a firm foundation never failing (Psalm 118:22; Isaiah 28:16; 1 Corinthians 3:11; Ephesians 2:19-22; 1 Peter 2:4-8). Jesus IS that foundation, "and underneath are the everlasting arms” of God (Deuteronomy 33:27). All I can say is: Selah!