What does Deuteronomy 30:15 mean?

It is not in heaven, that you should say, “Who will go up for us to heaven, and bring it to us, and proclaim it to us, that we may do it?”

Neither is it beyond the sea, that you should say, “Who will go over the sea for us, and bring it to us, and proclaim it to us, that we may do it?”

But the word is very near to you, in your mouth and in your heart, that you may do it.

For I command you today to love Yahweh your God, to walk in his ways, and to keep his commandments, his statutes, and his ordinances, that you may live and multiply, and that Yahweh your God may bless you in the land where you go in to possess it.

But if your heart turns away, and you will not hear, but are drawn away, and worship other gods, and serve them;

I denounce to you today, that you will surely perish. You will not prolong your days in the land where you pass over the Jordan to go in to possess it.