Article by R.C. Sproul – https://www.ligonier.org/learn/devotionals/proving-our-faith/
Read: Isaiah 58
The people of Israel, both the northern kingdom of Israel and the southern kingdom of Judah, went into exile because of their failure to trust and obey God (2 Kings 17:7–41; 2 Chron. 36:15–16; Isa. 1–5; 39). Restoration, therefore, could happen in only one way—God had to provide an atonement for sin that would make His people into the servants they were always supposed to be. If even holy Isaiah needed cleansing to serve the Lord (Isa. 6:1–8), how much more did the people in their evil need this atonement?
At this point in redemptive history, we look back in faith at that atonement, which occurred through the sin-bearing Messiah’s death under His Father’s judgment on the cross (1 Peter 2:24–25). Isaiah looked forward to this work (Isa. 52:13–53:12). Yet we cannot miss his prediction that the perfect offering of the Messiah would have cosmic ramifications beyond the gracious salvation of His people. Creation itself would rejoice at God’s work of making a sinful people into His holy people without compromising His righteousness. The earth itself would rejoice as the elect received their salvation because, as the Apostle Paul later wrote, this salvation would mean the world would not forever suffer the futility inflicted upon it by the fall of mankind into sin (55:12–13; Rom. 8:18–25).
Since salvation has cosmic ramifications, it must impact everything, and if those who profess to be saved evidence no change in their lives at all, their profession is empty. That is the prophet’s essential point in today’s passage. Because the Messiah’s atonement makes sinners into the Lord’s servants, the people of God cannot just sit idle. Isaiah foresaw that the post-exilic community would have some difficulty understanding this. The people would go through the motions—abstaining from food to show their dependence on God—but not really mean it—they would hurt others, thereby “abstaining” from obeying God’s Word (Isa. 58:1–5). Given the choice between fasting and not living out the ramifications of salvation by loving our neighbors, the Lord would rather we serve our neighbors and not fast (vv. 6–12). Of course, this is a false dilemma, for true fasting should lead us to see our dependence on God and His Word, and then do His will. Isaiah speaks in hyperbole for maximum effect. He means that fasting and other practices of piety are worthless if we do not serve our Lord and neighbors, because a failure to love our neighbors proves our faith is false (James 2:14–26; 1 John 4:20).
Our good works do not get us into the kingdom of God, but they do evidence the authenticity of our faith. We cannot rely in any way whatsoever on these works if we want to see God, but if we do not have good works, we do not have the trust in Christ alone that justifies us and therefore lays hold of eternal life. We must distinguish faith and good works, but we must not separate them. Faith always and necessarily gives birth to good works of gratitude.