"...when it is full grown, it is larger than the garden plants and becomes a tree,
so that the birds of the air come and nest in its branches."
A beautiful and well-functioning garden will have a variety of plants.
It will have the aged plants, such as trees that have been around a long time. These plants bring stability, shelter, protection. They give insight because their vision is greater because of their stature. They are a landmark, providing guidance and boundaries.
A garden will also have new growth. The fresh and new tastes and smells bring new hope and joy. However, these new and tender plants need the protection of the old. If the old is critical of the new, the garden will eventually die. The new plants need to be nourished properly or there may be defects in them when they become aged plants. However, God's grace is so great that He can turn the faults into unique identities.
A garden will also have the middle growth plants that are in between the old and the new. This is where a lot of the provision will come from. The day in and day out function of the garden will be here. When immature they may not understand that the fruit they produce will provide for the old and the new, however as their fruit matures they will see it.
Not only is the garden full of living plants, but creatures such as birds. For the new growth, the birds are a threat. Birds will devour the new seed that is not protected, thinking its food for them. But when the seed is cultivated--nourished and protected--it will grow and the birds are no longer a threat. As the seed turns into a plant that bears fruit, it feeds the very birds that tried to devour it. Now, because of its maturity, the birds can eat the fruit from the plant without killing it. The plant needs to give, and the birds provide that opportunity. Then, as a full grown tree, it provides a nesting place--a home--for the birds. The seed which was once threatened becomes a home to the very thing that threatened it simply because it was nourished, protected and grew into maturity where it could fulfill it's purpose.
What an awesome example the garden is of God's Kingdom.