John Gill Commentary Luke 12:5

"But I will warn you whom ye shall fear: Fear him, who after he hath killed hath power to cast into hell; yea, I say unto you, Fear him." — Luke 12:5 (ASV)

But I will forewarn you whom you shall fear ,
I will be your monitor, and direct you to the proper object of fear and reverence, and whom you should be careful to displease and offend:

fear him, which after he has killed ;
your body, as the Persic version adds; has taken away the life of it, by separating soul and body asunder, by sending one disease or another, or death in one shape or another:

has power to cast into hell ;
your soul, as the above version also adds; yes, to destroy both body and soul in hell, as in (See Gill on Matthew 10:28)

yes, I say unto you, fear him ;
and none else, not with a servile, but with a filial fear.