That explanation will require many patient repetitions. You can’t expect him to get the idea all at once. Chances are he is feeling some jealousy about the new baby, and that probably increases his need to have you play with him. It is especially important during this period that you find time to do special things with him and not simply put him off all the time. Right now, he probably needs reassurance that he is still important to you as much as he needs you to play with him. He will soon get used to the routine of caring required by a new baby and will let up on his demands. And find ways to praise him for being a big boy. Say things like, “I don’t know what I’d do if you weren’t so big and so able to do things for yourself these days.”
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.