This saying or scripture is in the bible. The spectrum has this simplified: Salt is used to enhance flavor, and as a preservative. To 'be salt' means to deliberately seek to influence the people in one's life by showing them the unconditional love of Christ through good deeds. Light is a symbol used to mean awareness, knowledge, and understanding.
You don't have to be religious or even spiritual to look at this saying as something special. The way i look at it is be someone's pick me up, make someone's day, just be kind for no reason. Influence one another's lives by showing them unconditional kindness and understand that we don't know what someone else is going through.
If this man that I never got the chance to really know left anything for me and the people's lives he would've impacted:
Be Salt and Light