Mood really matters a great deal, even in the Bible. And here I don’t mean any moodiness, tempers or emotional swings.
I speak about the grammatical mood. The most common and best recognized moods are: the indicative “You are light.” the imperative, “Be light!” and the conditional - “We would be light after it gets dark.”
There are many more verbal moods such as interrogative - “Are you light?” the potential verbal mood - “We may be light.” the optative mood - “If only we were light!”, the jussive “You shall become light.” or the exhortative - “Let us be light!” These are just the most common verbal moods and you can see how substantially they can transform the meaning of the verb.
Shortly after my arrival in Edinburgh as a student with only limited comprehension of spoken English, I attended a church and was surprised that the minister preached so passionately about lettuce! Soon I realized he was not an ardent gardener or salad chef. His interest in lettuce was actually caused by his proclivity for using exhortative “let us...”.
When Jesus said to his audience (not only to his disciples, but also to common folks) “You are light.” He did not command, “Be light!” He did not encourage “You should be light.” Nor did he threaten, “You should rather be light!” Jesus used the plain indicative mood in clear declarative power, he said “You are light.” It was a declaration, an affirmation, an EMPOWERMENT.
Unfortunately, as early as the time of the writing of the gospels, people did not sustain this power of Jesus’ statement and diluted it by attaching several exhortations. Clearly, Christians and especially preachers have this horrendous propensity to exhort, to form salad churches, with salad worship and salad theology, full of moralizing “lettuce - let us...” (Who could be surprised that they are so often so easily tossed even by the weakest trends, and dosed with spiritual sourness?)
Jesus did not exhort, he did not threaten, he declared, affirmed and EMPOWERED all those who were marginalized, vilified, persecuted and oppressed nobodies - YOU ARE LIGHT!
Let us heed and follow him! ;-)