The Mekhilta takes three words — "I, the Lord" — and unpacks from them a theology of divine certainty that spans from punishment to reward. When God declares "I, the Lord" in the context of the Exodus, He is doing something that no human authority can do: making a promise that is simultaneously an oath and a guaranteed outcome.
"What flesh and blood cannot conceptualize" — this is how the Mekhilta characterizes the divine declaration. A human king can promise punishment, but circumstances may intervene. Armies may fail. Allies may defect. The target may flee. God faces none of these limitations. When He says "I, the Lord," He is swearing by His own nature that the punishment He has announced will be carried out. The oath and the execution are the same thing.
Having established this principle in the context of punishment, the Mekhilta immediately pivots to beneficence using its signature kal va'chomer. Punishment, the rabbis repeatedly emphasize, is God's lesser measure — the mode He employs reluctantly, when justice demands it. Beneficence is His greater measure, His preferred mode of engagement with the world. If God absolutely guarantees His punishments, how much more absolutely does He guarantee His rewards!
The logic creates an extraordinary asymmetry. Divine punishment is certain — but divine reward is even more certain. If you can trust that God will follow through on consequences, you can trust even more deeply that He will follow through on blessings. The Mekhilta transforms a terrifying declaration against Egypt into a source of limitless reassurance for anyone who serves God faithfully.