Plz explain speaking order

In simple terms, a speaking order is an order that speaks for itself. The order should stand the test of legality, fairness, and reason at all the higher appellate forums. That is, the order should contain all the details of the issue, clear findings, and a reasoned order.

Source : Lawyers Club India

but what is the need or logic behind issue of speaking order in the above mentioned situation?

The need is that the the valuation of imported goods or goods to be exported is different than the self assessed value furnished by the importer/exporter, and since it may also include those situations where the assessment done by the officer is not accepted by the importer/exporter, so the officer has to justify the same and give a reasoned order so that the same can be explainable to other appellate authorities if the importer/exporter wishes to oppose it.