This chapter presents a happy cirecle. It opens reminding us of the great love God lavished on us to make us his children. Just imagine it! We deserved to be crushed as enemies, yet he chooses to set his love on us and make us children. And, were told in 1 John 3:2, that it gets better than this and we don't really know how good it will be.
Having been loved like this, we should love one another. The proof of having received the love of God is that we love one another (1 John 3:14).
God confirms that you belong to him. He does it when you keep His commands. Assurances of belonging to God and being on your way to heaven do not come from wishful thinking, but from submitting to Jesus.