v.1. To bring something into a close or effective relation with something: The college tied its fundraising campaign in with the alumni reunion. The pattern on the carpet ties in all the different fabrics in the room. In this paragraph, the author reviews the main points and ties them in.
2. To have a close or effective relation with something: The music should tie in with the holiday theme. If you make a remark during the lecture, the professor will discuss it as long as it ties in.