When it comes to serving the poor, what Jayakumar Christian says here, I think, is vital.
"The concrete expressions, or symptoms, of poverty are familiar to us all - social and economic deprivation, low income and unemployment. The causes of poverty, however, are flawed relationships. Poverty is about the oppressive relationships between the poor and the non-poor - how the poor and the social systems relate, and how the poor relate to civil society and government. Within the context of these flawed relationships, power is abused. This abuse of power is then expressed in low income, lack of food security, lack of nutrition and all those usual ways we measure poverty." (Excerpt from Another Way to Love, edited by Tim Costello and Rod Yule; Dr Jayakumar Christian is National Director of World Vision India.)
The ultimate cause of power abuse and unjust systems is of course sin. It is not only that individuals (including Christians) sin, there are also unjust social, economic, religious and political systems that are oppressive - even though some individuals in those systems are godly people. Christians must learn to recognise the existence of these systems and learn to discern who abuse power in those systems. (And sometimes we can be - unknowingly - involved in those systems.) We need to name them and seek ways to deal with them with God's help.
A heart of compassion and generosity are good and important. But they do not deal with the cause of poverty and injustice. Three examples in the Bible will help us here.
(1) The story of David, Bathsheba, Uriah and Nathan (2 Samuel 11:1-12:15). Here the sin of David is not just adultery and murder, but the abuse of his power. He who is in a position of power uses it to take someone's wife through an act of violence. The prophet Nathan's parable is telling, for it is about a poor man's own possession (an ewe lamb) being taken by a rich man who has plenty of flocks. The narrative here demonstrates that all sorts of (individual and social) interconnected evils exist through the abuse of power.
(2) Naboth's vineyard (1 Kings 21:1-29). Here Naboth refuses to give his vineyard to king Ahab because it is the inheritance that Yahweh has given his household. According to the Law of Moses, Israelite households are not to lose the land Yahweh has given them as a gift. But Ahab uses his power (via Jezebel) to kill Naboth and take his possession. Power is abused by someone in a position of power. The powerless person loses his possessions and his life. Here is a good example where compassion and generosity alone do not deal with the cause of injustice. Sin and power dynamics are at play.
What the prophets Isaiah, Amos and Micah say explicitly against social injustice are said implicitly by the two stories above.
(3) The story of the rich man and Lazarus (Luke 16:19-31). Here the rich man is considered wicked, while the poor man is seen as righteous. (This is of course where the Sermon on the Plain in Luke 6:20-26 makes sense.) To understand the story one has to read what Jesus has to say just before he tells the story. (Take a look at Luke 16:14-18 and you will see!) One thing that comes out from the story seems to be: The rich and powerful fail to understand the value system of the kingdom of God, despite the fact that they have the Scripture; but God shows mercy to the poor and powerless. (See my other article here for more about the rich man and Lazarus.)
In each of the above stories we see power imbalance. All too often human's desire for more stuff manifests itself throught a web of sin, social evils and oppression against the poor. This can happen in a local village in a low-income country, where the rich locals oppress the poor in the land. This can also happen when those who live in rich countries are unwilling to care for the poor in the world.
(It must be noted that none of what I said above means that the rich are more sinful than the poor. All have fallen short of the glory of God, and all need the grace of God for salvation. But the above highlights the complexity of our broken world, and what can be done about it when it comes to poverty and injustice.)