How can anyone know for sure they are going to heaven?

First of all, the Bible promises that you can know for sure, and because the Bible is reliable and God’s Word then the promises can be trusted. Plus, the Bible tells us that God has placed His Spirit in those who believe in Him.

How can anyone know for sure they are going to heaven?
After witnessing to a family member and telling them about your salvation they say, “It’s great that you’ve found something that works for you.”  How would you respond?
How would you invite a friend to your church and what would you say?