I am having difficulty understanding Galatians 3:16. Can you help please?

please read carefully gen.17;17-19 ' i will keep my covenant with HIM and with his descendants.' here 'him' refered as abraham's son ,that son is also considered as jesus.the verse has two fold meanings. one is abraham's only son issac ,god's only son jesus.but god make covenant with Abraham's descendants. that is descendants of promised son all the faithful