Basically God told Israel that if they would follow after Him (generally) then He would secure the Promised Land (Canaan; Palestine) in their hands. But, if they were to choose idolatry and sin, well, then He promised to remove them from their land, drive them into a foreign land and curse the ground in Canaan for their sake. And, we can see even in modern times that the land which once "flowed with milk and honey" is not even remotely that luscious today. In fact, much of it is barren. It was once densely covered with greenery and fruit. But, the sins of the people caused that blessing to be lost.
In the midst of the explanation of the land grant that God was offering to Israel, 3 great theological statements are made in Deuteronomy 29:2, 3 & 4, 29:29 and 29:19 & 20). These 3 statements are both deep and interconnected. What Moses was discussing was God's revelation of Himself and His truth. First, that nobody can understand anything about God until He reveals it to them. We are at His divine mercy. Second, there are some things about God that we will never know, but He has shared a few things with us for the very specific purpose of developing humble obedience in us. Last, if we think we can go our own way and do our own thing and still reap the benefits of obedience and righteousness... well, we have another thing coming. There will be a rude awakening for folk who imagine that wickedness will not go unpunished or that salvation is nothing more than a good insurance policy to be cashed in at the end of our self-centered and self-serving journey through life. Galatians 6:7-8 is a good reminder for us all!