What lesson about our society do you think Lowry is trying to teach in The Giver?

As Jonas experiences a range of complex emotions, it becomes apparent that human connection is much more profound than it is structured to be within his community. As Jonas is passed down memories of family and starts to experience love, he realizes that humans need love to be truly connected to one another. Without love, life is essentially meaningless. Without emotions—both positive or negative—humans cannot experience life fully.
The community in which Jonas lives operates on the ideology of Sameness. The Committee of Elders indoctrinates individuals into believing everyone is the same, and that Sameness is the basis for equality. While this appears to have created a Utopian society from the outside, Jonas comes to understand that a system of oppression is in place to establish Sameness, and that diversity among members of a community should be regarded as a strength rather than a weakness to be eliminated.
In order to maintain the supposed Utopian society in The Giver, community members are completely isolated from the outside world. This furthers the objective of indoctrination and, along with punishment by death, establishes unquestioning obedience of authority. The elements of totalitarianism and lack of free choice in the novel parallel certain societies that have existed or do exist today. The Committee of Elders operates on the principle of (what it believes to be) the greater good of its people; in reality, it has suppressed many truths, to the extent that the community cannot even comprehend all the elements of life that have been taken away from them.
In an age of globalization, multiculturalism, and racial integration, perhaps it seems as though modern principles of democracy would never be abandoned in favour of dictatorship. Yet The Giver does show us certain mechanisms by which it could be accomplished. One example is the implementation of the illegality of going to Elsewhere. Think of how censorship and strict internet controls can create a vastly different perception of the outside world, as is the case among individuals living in North Korea. Isolationism is an extremely effective tool in sustaining a totalitarian state.
Lowry's novel shows us that suppression of what makes us fundamentally human turns life into a meaningless, grey expanse. Yet these same elements of humanity also start wars, enable genocides, fuel racism, and propagate xenophobia. Human existence is filled with emotions, both positive and negative—thus, limiting emotions entirely is to not be human at all.