I'll explain that combat will be infrequent, and won't happen every gaming session...and the combat that does happen will have lower stakes. I'll tell them that we are going to be using milestone leveling, and that rewards are going to be based on how well they roleplay their characters' Bonds, Goals, Ideals, and Flaws. How many monsters they kill, or how quickly they can kill them, will never be in the spotlight.
And most importantly: I'll explain that things like paladin Oaths and warlock Patrons aren't going to be hand-waved, they are going to be primary and recurring focal points for the characters, and plot hooks for the whole party. Your bard belongs to a College, so over the next 20 levels, we are going to meet your headmasters, we are going to explore your campus, we are going to meet rival students and mentors, etc.