That first rest is a protein rest. Unless you are using a high percentage of unmodified grain (flaked or unmalted wheat, rye, oatmeal) it is not necessary.
The rest at 140 encourages high fermentability, Belgians are generally pretty dry which is why many recipes have sugar in them.
The rest at 150 is kind of middle of the road between fermentable and unfermentable sugars, although I think it still favors fermentables.
You could probably get away with a single infusion at 148-150 and use about .5 lbs of Carapils to help with the dextrins.
Something is always fermenting
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