In this context, when someone says "Let's wrap up this lesson," it means they are suggesting that the lesson should be concluded or finished. So, #1 means the same as #2 - "Let's finish this lesson." "Wrap up" is a common informal expression that means to bring something to a close or to complete it. It implies that you are reaching the end or conclusion of a particular activity or event. The phrase "Let's summarize this lesson" in #3 suggests a slightly different meaning, as it specifically refers to summarizing the main points or key takeaways from the lesson, rather than simply finishing it.