What are three phases of tree in poem ? What it teaches us?

So,The first phase where there is full of silence in the laburnum tree (yellow in colour) it's colour depicts beauty and silence. Second phase where the goldflinch bird stis on the branch of tree and started feeding her children as it is fueling the trees engine and the tree is no longer that silence and creepy it is moving it's leaves as the tree is happy. And the third phase where the bird landed off the tree which brings again to it original state. It teaches that life brings you down and brings you at top but never give up.