Boy Scouts have a law that they learn early in their scouting life. The introductory statement to the law is, "A scout is." The attributes that make scout law; trustworthy, loyal, helpful, friendly, courteous, kind, obedient, cheerful, thrifty, brave, clean, reverent.
I know that I am never all of these things at all times, but I've also learned over the years that I need a calling related to my identity, even if I'm not able to fulfill it.
Jesus does something similar. In his Sermon on the Mount, Jesus tells his followers, "You are salt," and "You are light." Salt preserves and makes life taste better (forget the salt fears of today). Light helps all people see. You may not take on all of the attributes of salt and light every day in your life, but Jesus doesn't say, "be salt, or else." This is not a warning, but a continual reminder of our identity, something that we are called to live every day, like breathing. Simply put, Jesus tells us, "you are." Our lives as light and salt become living evidence of God's love in the world through Jesus.