He committed no sin, neither was deceit found in his mouth. When he was reviled, he did not revile in return; when he suffered, he did not threaten, but continued entrusting himself to him who judges justly. He himself bore our sins in his body on the tree, that we might die to sin and live to righteousness. By his wounds you have been healed. For you were straying like sheep, but have now returned to the Shepherd and Overseer of your souls.
1 Peter 1:22-25
Comfort, comfort my people, says your God. Speak tenderly to Jerusalem, and cry to her that her warfare is ended, that her iniquity is pardoned, that she has received from the LORD's hand double for all her sins. A voice cries: "In the wilderness prepare the way of the LORD; make straight in the desert a highway for our God. Every valley shall be lifted up, and every mountain and hill be made low; the uneven ground shall become level, and the rough places a plain. And the glory of the LORD shall be revealed, and all flesh shall see it together, for the mouth of the LORD has spoken." A voice says, "Cry!" And I said, "What shall I cry?" All flesh is grass, and all its beauty is like the flower of the field. The grass withers, the flower fades when the breath of the LORD blows on it; surely the people are grass. The grass withers, the flower fades, but the word of our God will stand forever. Get you up to a high mountain, O Zion, herald of good news; lift up your voice with strength, O Jerusalem, herald of good news; lift it up, fear not; say to the cities of Judah, "Behold your God!" Behold, the Lord GOD comes with might, and his arm rules for him; behold, his reward is with him, and his recompense before him. He will tend his flock like a shepherd; he will gather the lambs in his arms; he will carry them in his bosom, and gently lead those that are with young.
The Story of Isaiah 40
After announcing comfort, the ending of warfare, iniquity pardoned, the prophetic announcement of the coming Messiah and all flesh seeing Him, the Lord reminds these people of he difference between the power of men and the power of God.
Into that overwhelming discouragement, the Lord speaks reminding the people of His power even in the face of seemingly unstoppable superpowers...He is God.
The Relevance of Isaiah 40 in 1 Peter 1:22-25.
We, the people of God, by our birth as new creatures in Christ, are now strangers and exiles in this world, and we can also find ourselves discouraged if we do not stay focused on our God and His unchanging decrees.
We wait for the coming of our Lord, confident that He will return, tend his flock like a shepherd, gather the lambs in his arms, carry them in his bosom, and gently leads them.
As those not belonging to this world, we remember that regardless of what man may say, it is the Lord's Word that stands and controls our lives.
How does this passage relate to brotherly love?
Because we are strangers to this world, members of the Kingdom, and a true ethnicity of God, we have much more in common with the people of god than we do the people of the world.
As the body of Christ, we comfort and encourage the people of God with the Word of God.
The Word preached to us is the Word of God in which He has decreed full and final salvation when we will be sinless and perfect brothers and sisters in Christ.
...while Moses went up to God. The LORD called to him out of the mountain, saying, "Thus you shall say to the house of Jacob, and tell the people of Israel: You yourselves have seen what I did to the Egyptians, and how I bore you on eagles' wings and brought you to myself.
Now therefore, if you will indeed obey my voice and keep my covenant, you shall be my treasured possession among all peoples, for all the earth is mine; and you shall be to me a kingdom of priests and a holy nation. These are the words that you shall speak to the people of Israel."
Take care lest your heart be deceived, and you turn aside and serve other gods and worship them; then the anger of the LORD will be kindled against you, and he will shut up the heavens, so that there will be no rain, and the land will yield no fruit, and you will perish quickly off the good land that the LORD is giving you.
Now the works of the flesh are evident: sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions, envy, drunkenness, orgies, and things like these. I warn you, as I warned you before, that those who do such things will not inherit the kingdom of God. But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law. And those who belong to Christ Jesus have crucified the flesh with its passions and desires.
...since you have been born again, not of perishable seed but of imperishable, through the living and abiding word of God
1 Peter 1:23