Prayer for a miracle and for the past

Hello Rabbi,
The verse in the rel sign writes, "He who enters to measure his grain says, 'May it be pleasing to You, O Lord my God, that You send a blessing upon this field.' He began to measure, saying, 'Blessed is He who sends a blessing upon this field.' He measured and then blessed the seventh. It is a vain prayer, for the blessing is not found except in something hidden (i.e., the unseen and not seen) from the eye.' I did not understand why before the measurement this is not a vain prayer? And after all, we do not expect things above nature. And if we are not talking about a quantitative change through the blessing, but rather about the business succeeding, such as the grain becoming more expensive, why does this not belong after the counting?