This is a little broad for an enotes answer considering the volume of Heaney's work overy many years. One possible approach is to look at the poems about childhood which attempt to make sense of the world. There's nothing unique in this as all children have to make sense of the world in which they are growing up. Take a poem like 'The Early Purges' for example. The boy is witnessing death for the first time, seeing its starkness and finality but also trying to absorb the matter-of-fact, unfeeling way in which the creatures are killed. The crude language is meant to reinforce the hard shell that 'real men' are supposed to develop in dealing with such matters. Or in a poem like 'Blackberry Picking', he is learning about hope and disillusionment. Even the title of the volume 'Death of a Naturalist' suggests that the poems express disillusion about the natural world, the harsh realities behind apparently attractive things.