When Someone is telling you something in great details and you want to find out what they are going to indicate at last, you would ask them to cut the matter short and tell you the main subject (perhaps their purpose) and let you know what they intend to say in short and avoid giving you more details about the topic under discussion.
I have found an idiom and a word, but I have no idea if using them this way would sound natural to you:
Please tell the heart of the matter.
Please tell the gist of the matter.
If not, then let me know what shall I say instead.