The separation between leading and showing mercy is not telling us that leaders can not be merciful or that people who show mercy can not be leaders! Paul, here, is merely going through these ideas to say that whatever we are called to do we must do it for God.
In the Psalms we often see David, the individual feeling hopeless. Here it is a whole nation. But it was not God's intention to leave them in their hopelessness. He saw their misery, and wanted to revitalise the sad discouraged community of Israel. There are many groups, churches, communities and nations today who need to know that the Lord can make dead bones live.