The prophets of old always spoke of the burden of the Lord. Their hearts were weighed down by God as He shared the sadness and grief that He had over His rebellious people.
Their sin completely drove God from them, and caused His heart to ache in the same way parents feel when their children rebel against them. It is the same hurt a husband has when his wife cheats on him. The agony is real and so it is with our Creator.
The Holy Spirit shares His heart with Christians today which burdens the intercessor to bow down under the weight God shares with them driving them to pray for the wicked and step into the role of trying to bring their neighbors to repentance. Revival is a result of God pouring out His heart and influencing His people to pray.