N.B. the Bible addresses this issue directly in Amos, who decries the lack of social justice (5:24).
"Where there is no vision the people perish..." (Prov. 29:18 KJV). N.B. a church has a mission to the un-churched and a ministry to its congregation. We are all ministers and should all be on a mission. Many believers confuse works and faith not realizing that works are not a replacement of faith, but the fruit of it. Faith without works is dead according to James 2:17 and dead faith saves no one. We need people of social concern, but this is not the primary function of the church--discipleship is.
However, the faith you have is the faith you show, they say. We are not saved by works and we are not saved without works either. We are not saved by service but unto service. If we have no good works, our faith is suspect or spurious. Eph. 2:10 asserts that "we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them." We don't want to be like the Cretans: "They profess to know God, but by their works they deny Him." True faith yields fruit: no fruit, no faith. John 15:16 says, "But I chose you and appointed you that you should go and bear fruit and that your fruit should abide...." Again: "And let us consider how to stir up one another to love and good works" (Heb. 10:24). The danger is that there will be some who are converted to the program but not to Christ. To sum it up, the Reformation formula was that we are "saved by faith alone, but not by a faith that is alone."
This terminology became popular in the era of social change in the 20th century from so-called fundamentalists. There really is no "social gospel," but one gospel message: the preaching of Christ in His death, burial, and resurrection on our behalf. Papists (Romanists) are very earnest and sincere in doing good deeds for the less fortunate, like opening soup kitchens, hospitals, schools, and orphanages, et al. However, they are misguided as to the plan of salvation. Evangelicals are very good at preaching the gospel, but of neglecting the application and further responsibilities of the church (like caring for the widow and orphan which are commanded).
We are all light and salt; the church is the vehicle or instrument of grace in the world. We are to keep the main thing the main thing, and not major on the minors (the Great Commission is where it's at and is to be our focus).
God isn't looking for a church of do-gooders or works-oriented believers. But we need to be people on a mission to be sure. We need not be remiss in our duty to our fellow man and offer a cup of water in the name of the Lord, as it were, with our gospel message. Taking care of the needs of the poor is an open door to preach and gives us the opportunity to spread the Word (our goal). It is not the mandate of Christ to convert us to one philosophy or political persuasion or viewpoint: God loves us despite this. Jesus is not going to inquire of our political aspirations or beliefs at the Bema ( the Judgment Seat of Christ). "He pled the cause of the afflicted and needy; Then it was well, Is not that what it means to know Me? says the LORD" (Jer. 22:16). Do we indeed know Him, whom to know is eternal life (cf. John 17:3)?
I do not believe He is even going to ask us if we are Arminian or Reformed in our interpretation of Scripture. However, He is going to say," I was hungry and you gave me something to eat, I was thirsty and you gave me something to drink, I was naked and you clothed me, and I was in prison and you visited me." Christianity is not a philosophy, but a relationship with a living Lord (and this has become a cliché) but, nevertheless, it is vital that our faith doesn't vanish into a religion of do's and don'ts, or a duty done out of obligation, rather than love as a high calling and not as duty (God sees our motives).
In Mal. 3:5 God is "against those who oppress the wage earner in his wages" and who "thrust aside the sojourner". God is indeed concerned about social issues (there are many social injustices that one could get concerned about privately) and it may be the calling of individual Christians to go on a crusade (e.g., against child labor or slavery), but this is not the calling of the church at large.
Great Christians like William Wilberforce have influenced the end of slavery as we know it in the free world. The job of the church is to make disciples of all nations and teach them to observe all that Christ commanded (cf. Matt. 28:19-20). n sum, there is a social commission, not a social gospel, that has not been rescinded but we are to keep the main thing the main thing and not get sidetracked by turning loaves into bread. Soli Deo Gloria!