I've been pondering about it. During one of my devotions, I got an answer: it is God who heals. I have doubt because my focus is on the song which heals, and I did not focus on God who heals. I believe all those who had been healed either from singing this song or just listening to it, was healed by God. It is not the song which heals, but God. By saying this, I am not saying or encouraging people to simply write songs to manipulate people psychologically, but songs must be written firstly through the meditation of the Word of God and with our experiences with God. This is what is lacking in today's Christian songs!
Question came now, will I use the song in church. My stand is, I will not! Because it is God who heals by His grace and His will. Our focus should not be with the power of the songs, but our focus must be with the power of God who heals!