It's significant, I think, that Scripture states that Jesus saw the people and as a direct result of his seeing, felt compassion on them. I think there is something to seeing people in their need, whether a large crowd or individual that stirs up compassion in our hearts, even the Lord Jesus' heart. It's just a part of the way God wired us (to whatever degree we still reflect his image). God has compassion, and so should we. But it helps to actually see people.
In an airport the other day I couldn't help but be stirred up to prayer and an evangelistic spirit. The people were so needy! You could see it on their faces, in their manners, in their clothing even. High society types and Joe Blows. All needed God. Even upon meeting certain professing Christians I was stirred up seeing and feeling the godlessness of the world that surrounded us all in that crowded place. If I would not have been there, I don't think I would have prayed those prayers or had the same heart and spirit.
Here are some other verses:
Matthew 14:14
When He went ashore, He saw a large crowd, and felt compassion for them and healed their sick.
Mark 6:34
When Jesus went ashore, He saw a large crowd, and He felt compassion for them because they were like sheep without a shepherd; and He began to teach them many things.
Luke 7:13
When the Lord saw her, He felt compassion for her, and said to her, "Do not weep.
Luke 10:33
But a Samaritan, who was on a journey, came upon him; and when he saw him, he felt compassion,
Luke 15:20
So he got up and came to his father. But while he was still a long way off, his father saw him and felt compassion for him, and ran and embraced him and kissed him.
I think it would be good then to seek out times of being with those in need. In crowded places like malls and airports, or in smaller places like coffee shops or spending time with a lost friend. If your heart is cold and dry, put down your theology book and take a prayer walk where you can see some people. The hope is that God would stir your heart like he did Christ's when he walked this earth.
Can compassion be stirred up without the act of seeing? Sure, Paul prayed fervently for people and churches he had never met face to face. But it takes rock solid faith. I think seeing helps.
O God, please open our eyes to the world around us. Don't let us focus on ourselves and get bogged down with daily affairs. Give us sober minds and heavy, loving, hopeful hearts. Amen.