This is based on the principle that the otherwise superfluous accusative article "et" always conveys some additional teaching (Pesachim 22b).
ðɪs ɪz bˈeɪst ɔnðə pɹˈɪnsɪpəl ðætðɪ ˈʌðɚwˌaɪz suːpˈɜːfluːəs ɐkjˈuːzətˌɪv ˈɑːɹɾɪkəl "ˈɛt" ˈɔːlweɪz kənvˈeɪz sˌʌm ɐdˈɪʃənəl tˈiːtʃɪŋ pˈɛsætʃɪm twˈɛnti tˈuː bˈiː.