Are you thinking that "let" means "allow"? Like, "Allow me to laugh, please." I think "let" often means an exhortation. Like, "Let's have some fun!" It can mean "allow", of course, but I don't see that in the verse you quote.
Webster Dictionary - LET - to cause to : MAKE When God was creating earth, water, light etc, His words were 'let'. It was a command more then a request 'allow' meaning. All thru out the Bible word 'let' in most cases met an action, a command, an instruction... Matthew 27:42 (KJV) He saved others; himself he cannot save. If he be the King of Israel, let him now come down from the cross, and we will believe him. (word let used as challenge - 'try to' come off the cross )Mark 4:9 (KJV) And he said unto them, He that hath ears to hear, let him hear. (word let used as a command - have to hear)John 7:37 (KJV) In the last day, that great day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink.(word let used as plea - please come)Romans 12:9 (KJV) Let love be without dissimulation. Abhor that which is evil; cleave to that which is good. (word let used as 'no exception' - has to be this way)1 Corinthians 1:31 (KJV) That, according as it is written, He that glorieth, let him glory in the Lord(word let used as a result of an action - if.... then....)