The film starts with a near-silent precis of the plot and themes - cuckoldry and the exhaustion of life on the road. But the characters are more interesting than that. Albert is a immature free spirit, whose wife prefers the comfort and stability (and income) of running a tobacconist. In one of the most powerful scenes in the film, she denies her husband the right to come back into her life. She will not compromise her freedom.
Albert is a child. The final scene comes back to the cuckolded clown and introduces the idea of going back to the womb - finding some security with whoever you can, even if they have betrayed you. Albert's voluptuous mistress is enticed away by a fashionable actor, who tricks and rapes her. She is an innocent as well, but Albert mistreats her almost as badly. At the end of the film she has nowhere left to go but back to him.
Bergman has a lot of sympathy for the circus performers and spends some time on the snooty and condescending treatment they receive from the theatre troupe. Interestingly, Bergman started out in the theatre, so I wonder whether he identifies the film-making process to be similar to the circus - cruder, less well-respected, a haven for fools and innocents - and a more noble persuit as a result.