Isaiah 51:6
Lift up your eyes to the heavens, and look upon the earth beneath: for the heavens shall vanish away like smoke, and the earth shall wax old like a garment, and they that dwell therein shall die in like manner: but my salvation shall be for ever, and my righteousness shall not be abolished.
This world and everything in it is wearing out and passing away, while God's saving power and His right doing last forever and will never fail or be taken away. His right doing is His holy law, the expression of His own character, and those who belong to Him are those who know that right doing because His law is written in their hearts. It is a word of comfort and courage to those weighed down by pain and trouble, calling them to seek the Lord in prayer, turn from sin, and do what is right. It also strengthens those who suffer reproach and threats for obeying God rather than men, assuring them they need not fear, for their opposers will be eaten away like a moth-eaten cloth while God's salvation endures.
Passing World, Enduring Salvation
Lift up the eyes to the heavens and look upon the earth beneath to see how temporary all earthly things are, for the heavens shall vanish away like smoke and the earth shall wax old like a garment and wear away. The earth and its features are changing and wearing out with age, while its inhabitants shall die in like manner as mortal people passing away with it. The heavens and the earth and all who dwell therein stand in sharp contrast to what endures, since they are temporary and destined to pass while something greater remains.
In contrast to that passing world, salvation shall be forever and righteousness shall not be abolished and shall never end. That enduring salvation and unabolished righteousness belong to God, and His blessing and care for His people will never cease even as the earth ages.
Righteousness, Law, and Covenant
God's righteousness in the verse is His holy law, the transcript of His character. The context around it presents His law and His judgment going forth as a light to the peoples and His salvation going forth, and describes His people as those who know righteousness because His law is in their hearts. They need not fear human reproach, for their persecutors perish while God's righteousness and salvation endure.
The chapter teaches God's covenant with the people He seeks to save, the terms of salvation, and the education of greatest value. Its surrounding chapters are to be read alongside Isaiah 56 and Isaiah 58, which connect God's salvation and righteousness with keeping the Sabbath, honoring God, doing justice, and joining His covenant. In this setting the chapter is a plain scripture on the Sabbath question, showing that God has made no change in His day of rest and giving wonderful promises to those who obey His law.
Comfort and Faithfulness in Trial
The verse gives assurance and hope in the Lord to the afflicted, offering courage and comfort that should not be disregarded or misunderstood. It is exceedingly precious to read with assurance and hope in tedious affliction and pain. It shows that the Lord bears all human burdens, even while the heavens and earth pass away and their inhabitants die, because His salvation and righteousness last forever. That everlasting salvation is the help to be sought by seeking the Lord through prayer and confession, by repenting of sins and practicing righteousness, bringing comfort and encouragement to those who receive it.
It assures those who remain faithful to God amid persecution that human power and reproach are temporary, while His salvation lasts forever and His righteousness will never be abolished or end. They need not fear men when they face threats, reproach, reviling, and religious persecution for obeying God rather than human commands. Those who know righteousness and have God's law in the heart are people of genuine faith who love God, share in Christ's sufferings, and persevere in obedience. They refuse to sell their souls for money or human favor even when bitter opposition forces them to forsake houses and lands and relatives, with heaven on the side of Christ, and God will honor them and register them in the book of life.
Their persecutors and all who exalt themselves against God's will and work will perish, while God's righteousness and salvation endure. Like a garment eaten by moths and wool eaten by worms, they will pass away, and at the appointed time they will feel God's wrath. The chapter is to be brought to the front now and put before the people to do its important work in their hearts. It calls every worker to draw nigh to God and receive the sanctification of the Holy Spirit.