Charity is how I can actually help someone with my own money and time, and convert their soul to good ("You didn'thave to give that to me, and yet you did. Thank you!") and my soul to good (It feels good to make sacrifices for others.").
Social justice is how I can help someone with someone else's money, using the power of government to take money from people, which hardens the heart of potential givers ("I pay taxes! I don't have to give anything more.") and hardens the heart of the receiver ("These are entitlements. I'm entitled to your money!")
Social justice supporters forget that Jesus was not a lobbyist, and never asked the government to do anything.
Social justice supporters forget that Jesus did not come to improve the lot of the poor. Improving the lot of the poor through charity is a means to the end, not the end itself. Social justice supporters seek to make charity unnecessary, and thereby undermine one of the best, if not the best, ways to convert souls...through charity from all to all.