In Genesis 18:7; 2 Samuel 12:4, this symbolizes earthly goodness. (Arcana Coelestia 2181)

650. 'Length' means the holiness, 'breadth' the truth, and 'height' the good, of the remnants described by the numbers. This cannot be confirmed so easily from the Word because every single thing has reference to the particular subject or thing under discussion. For example, when 'length' applies to time it means perpetual and eternal, as in 'length of days' Psalms 23:6; 21:4, but when it applies to space it means consequent holiness. The situation is the same with 'breadth' and 'height'. All earthly objects are three-dimensional, but no such dimensions can be used in reference to celestial and spiritual things. When they are used to refer to these they mean the degree of perfection, greater or less, independent of the dimensions given, as well as identity and quantity. In this case they are identified as remnants, which are few in quantity.