ShivamOld is gold
The cake was a symbol of the initiation of the bond that was shared between Harvey and Inez Warninger. It would go down in the family and help in enriching the values they had imparted and the sacrifices they had made to provide love and care to the family.
Emotions matter 
This incident teaches us that emotions can come wrapped in anything big or small. It is not the size of an object rather than the depth of the emotions attached to it that matters in the end. If the bond is pure then it will find its way to survive and sustain even through the toughest of the times.