Therefore, strengthen the hands that are weak and the knees that are feeble, and make straight paths for your feet, so that the limb which is lame may not be put out of joint, but rather be healed.
lift up the hands — Whether your own or your brethren’s; which hang down — Unable to continue the combat; shake off discouragement, sloth, and indolence, and exert yourselves in your spiritual warfare, and in the performance of your duty; and strengthen, by faith and prayer, the feeble knees— Unable to continue the race. And make straight paths for your own feet — And for those of others; remove every hinderance, every offence out of the way; lest that which is lame — Those who are weak and feeble among you; be turned out of the way — Of truth and duty; but let it rather be healed — Let them rather be delivered from their fears and dejections, and be confirmed in their Christian course.
Paul is talking to all of his readers, the weak and the strong, to strengthen their faith so that those who are following would not stumble and fall. Like exhausted runners who lack the energy to make it to the finish line, many seemed close to collapsing on the sidelines.
The weak must find God’s strength (Heb 12: 2, 3) and quit entertaining in their minds the option of abandoning Christ, and the strong must take the initiative to strengthen the faith of those who are weaker. We cannot passively ignore those who are struggling and leave them to fall away. We need to snatch them from the fire.
And have mercy on some, who are doubting; save others, snatching them out of the fire; and on some have mercy with fear, hating even the garment polluted by the flesh.
This is a constant endeavor, no holiday, no time off! We probably have all become weary and tired in the effort of lifting and strengthening others. But God... God has shown us how to be effective in doing His work!
But you, beloved, building yourselves up on your most holy faith, praying in the Holy Spirit, keep yourselves in the love of God, waiting anxiously for the mercy of our Lord Jesus Christ to eternal life.
We are effective after building ourselves up by praying in the Holy Spirit, that is what keeps us in God's love, we don't have that naturally in ourselves. The only Good in us comes from God, Jesus said there is none Good but God. But! We have God in us! Don't grow weary in doing good, don't become frustrated, seek God, He will lead you to place, to the people, and give you the words to speak to strengthen weak hands and feeble knees. God builds up and He employs us to do the same so put on your hard hat (helmet of salvation) and keep building God's kingdom!