Hi Olya,
A broad topic, but also a hot one. In my experience the key question is always "WIIFM", so what will it bring your stakeholder? Looking at the different roles and really taking on board their perspective point out the real benefits. Depending on how you use Marketo that can of course be several things, like higher quality leads (so more easily meeting their targets), less bad lead (so less boring calls and admin), better insights into what is important to their lead (so better call quality and higher chance of conversion). For higher management it could have elements like better insights into successful campaigns and how they contribute to the bottom line, better budget control, etc.
Also important is how the feedback of your audience is important to drive success. Actively asking for feedback on campaigns and together drafting a seemless journey for the customer is a great success driver and an introduction session like this is a good chance to actively seek their engagement.
Hope this helps!
Katja