Suppose a believer is rich enough to have all the things he needs. He sees his brother {in Christ} who is poor and does not have the things he needs. What if the believer who has things does not help the poor brother? Then the believer who has the things he needs does not have God's love in his heart.
That is the way we know that we belong to the way of truth. And when our hearts make us feel guilty, we can still have peace before God. Why? Because God is greater than our heart (conscience). God knows everything.