The Iranian missile-drone attack was likely intended to cause significant damage below the threshold that would trigger a Israeli response, but was designed to succeed
The strike package was modeled on those the Russians have used repeatedly against Ukraine to great effect. The purpose of such a package is to have the slower cruise missiles and drones distract and overwhelm air defenses in order to allow the ballistic missiles, which are much harder to shoot down, to reach their targets. The Iranians very likely expected that few if any of the cruise missiles and drones would hit their targets, but likely hoped that a significantly higher percentage of the ballistic missiles would do so.
Ukrainian air defenses have averaged interception rates of only about 46% of Russian ballistic missiles during recent large strikes. The Iranians likely expected that Israeli rates would be higher than the Ukrainian rates but not above 90% against such a large ballistic missile salvo—the Russians, after all, have never fired close to that many large ballistic missiles in a single strike against Ukraine.
Israel and its allies employed hundreds of combat aircraft in this effort.[4] Ukraine lacks both of these advantages.[5] Iran also lacks access to the near-hypersonic missiles Russia has used to penetrate Ukrainian air defenses more reliably—at least for now.
Ukraine has, in particular, been unable to use combat aircraft to shoot down Russian drones and cruise missiles at scale
Iran will learn additional lessons from the failed April 13 attack that it can leverage to launch more successful attacks in the future. The lessons that Iran will draw from this attack will allow it to build more successful strike packages in the future. The attack probably helped Iran identify the relative strengths and the weaknesses of the Israeli air defense system. Iran will likely also share the lessons it learned in this attack with Russia. Russia will then use these lessons to improve its ability to defeat US- and NATO-provided air defense systems in Ukraine.
See also https://twitter.com/TheStudyofWar/status/1779655626404106734