According to Osho, you should reverse appearances: when he jokes he’s delivering his most serious truths, and when he sounds serious he’s playfully undercutting rigidity. He uses humor as a nonviolent way to say what would otherwise hit too hard. So don’t fixate on tone; listen for the underlying pointer concealed in laughter or solemnity.
When he jokes, he’s telling you something important; when he sounds serious, he’s also playing—so focus on the message, not the mood.