Compassion means to have intense emotions and feelings in our hearts seeing the sufferings of others, and to be willing to make sacrifices, even experience inconveniences for their welfare.
God’s nature is that He is supremely compassionate. Because we are part and parcel of God, we too have the same original nature of compassion. Therefore, as our consciousness becomes purified of material qualities, the prominent quality of the soul -of being part and parcel of God’s compassion, to be an instrument of God’s compassion, becomes manifest.
Philosophically, compassion brings real happiness. Why? Because the expression of compassion is so pleasing to the Lord, when we show compassion, the Lord is pleased and when the Lord is pleased we experience real happiness. The Srimad Bhagavatam draws the analogy of a tree to explain this phenomenon. When we water the root of the tree, every part of the tree is nourished, and this cannot be accomplished by watering the parts of the tree separately. Similarly the Lord, being the root of all existence and we being part and parcel of the Lord, the only way to find the nourishment of real happiness is by giving pleasure to the Lord.
How to reawaken this quality of compassion? There is only one way: through association, for we become like what we associate with. Srila Prabhupada gave an example to help us understand this. If we put iron rod in fire, it becomes red and hot like fire, and if you touch it, you get the same experience as you touch fire directly. When that same iron is put in ice, it becomes like ice. The law of nature is that we become like whom we associate with. When we associate with God, our godly qualities, of which compassion is a prominent one, awakens within our heart. And what is the best why to associate with God? To associating with those who love God.