We can do good in many ways. But God seems to also define “doing good” in particular ways through the prophet Isaiah: “Learn to do good; [in other words] Seek justice, Reprove the ruthless [“defend the oppressed” (NIV)], Defend the orphan, Plead for the widow” (Isaiah 1:17, NASB; see also Psalm 146:9; Isaiah 58:6-7; Zechariah 7:9-10; Matthew 23:23).
God wants us to contend for these people because he does: “I defend the cause of the fatherless and the widow, and love the foreigner residing among you, giving them food and clothing” (Deuteronomy 10:18, personalized; see also Psalm 146:9).
God delights in doing these acts of kindness, justice and righteousness: “Understand and know me, that I am the Lord, who exercises loving kindness, justice and righteousness on earth, for I delight in these things” (Jeremiah 9:24, personalized; see also Psalm 33:5; 89:14; 103:6). How much more is his delight when we join him in “doing good” in these ways.
Tim Keller summarizes this as follows:
“The Hebrew word for ‘justice,’ mishpat, occurs in its various forms more than 200 times in the Hebrew Old Testament. . . . Mishpat is giving people what they are due, whether punishment or protection or care . . . Over and over again, mishpat describes taking up the care and cause of widows, orphans, immigrants and the poor . . . Realize, then, how significant it is that the biblical writers introduce God as ‘a father to the fatherless, a defender of widows’ (Psalm 68:4-5) . . . (The Hebrew word for righteousness), ‘tzadeqah refers to day-to-day living in which a person conducts all relationships in family and society with fairness, generosity and equity . . . These two words roughly correspond to what some have called ‘primary’ and ‘rectifying justice.’ Rectifying justice is mishpat. It means punishing wrongdoers and caring for the victims of unjust treatment. Primary justice, or tzadeqah, is behavior that, if it was prevalent in the world, would render rectifying justice unnecessary, because everyone would be living in right relationship to everyone else.”