Jesus says you are the salt... and you are the light. He doesn't tell them to try to keep trying to be salty or to try to keep shining. How do we help people to see that if they are in Jesus they are salt and light? Consider the effect in two different scenarios: in one, I told someone to be strong or try to be strong, vs. in the other scenario I told him he is strong. Would the second scenario not be more encouraging and motivating? Are we out of sync with Jesus’ thought here if we focus primarily on action as we explain and apply this passage, say, to evangelism?
I think you are right. The gospel focuses more on what we are to be rather on what we are to do. You are right there. To say we already are something is partly true, but not fully. For example, Paul tells the Corinthians to be strong (1 Corinthians 16:13), right?
So, yes, but be careful... This is why my Shining Like Stars [now titled Till the Nets Are Full, 2018] had to be rewritten in 2006, 2010, 2015. Older versions (1987, 1990, 2000) were too mechanical, lacking grace. But this doesn’t mean the imperative for evangelism is done away with. Far from it! If we are light and salt, then not to share with others is not merely to disobey our master but to deny our very nature as new creations.
For more on this, see John 15, Philippians 3, 1 John 2, etc.