John Gill Commentary Joshua 23:15

"And it shall come to pass, that as all the good things are come upon you of which Jehovah your God spake unto you, so will Jehovah bring upon you all the evil things, until he have destroyed you from off this good land which Jehovah your God hath given you." — Joshua 23:15 (ASV)

Therefore it shall come to pass, [that] as all the good
things are come upon you which the Lord has promised you

Of which there was full proof, and it could not be denied:

so shall the Lord bring upon you all evil things ;

calamities and distresses, by his sore judgments of famine, sword, pestilence, evil beasts, and captivity, in case of disobedience to his commands:

until he have destroyed you from off this good land which the Lord your
God has given you ;

for as he is faithful to his promises, so to his threatenings; and from his punctual performance of the one may be argued and expected the sure fulfilment of the other, and which has been abundantly verified in that people; see (Leviticus 26:1–46) (Deuteronomy 28:1–68) and the notes there.