הלכה על חולין 120:73

The matter is known and famous that God, may He be blessed, moves all that exists and created man and put him in control over the earth and over every thing that is in it. And it is from His traits, Blessed be He, that He is of much kindness and that He desires the good of His creatures, and [so] He wants them to be fitting and meriting to receive goodness from Him. And this is really from His perfection, may He be blessed. As only one who gives to others besides himself can be called perfect in the good - there is no doubt about this to any intelligent person. And since [we are in] agreement [about] this, that we know that it is obligatory from the perfection of His goodness, that His desire is to pour down His blessing upon us, we shall say that the matter of the blessing that we say in front of Him is only a mention to arouse ourselves through the words of our mouths that He is the blessed One, and the blessed One that contains all of the goodnesses. And through this good arousal of ourselves and the designation of our thoughts to admit to Him that all of the goodnesses are included in Him and He is the King over them, to send them to all that He desires, we merit through this good action to bring from His blessings upon us. And after this mention and this admission in front of Him, we request from Him that which we need [of] knowledge, or the pardon of our iniquities, or healing, or wealth or anything. And so [too,] after the request from Him, we repeat and admit to Him about this, to say that it comes to us from Him. And this is the opening and the conclusion of the blessings. [The reason for the latter is that we not] be considered like a slave who took a reward from his master and goes away without permission, like a thief. And it comes out according to the premise [created by] this reason that "blessed" is an adjective, meaning to say it is an admission to Him that He contains all of the blessings. And [about] the expression, "may He be blessed," that we always mention - which is [in] the reflexive case - we can say that the intention of it is that we are supplicating to Him that it be His will in front of Him to cause the hearts of His creatures to be prepared in front of Him that all should admit to Him and praise Him. And this is the explanation of "may He be blessed," meaning to say, "It should be Your will in front of You, that all people of the world will relate all blessing to You and admit that everything in the world emanates from You," and that His will be completed - as He wants to do good, as we have said. And the fulfillment of the Will is the purpose of all that ask. And behold, we have found an explanation even for the puzzling expression of "may He be blessed." And from this understanding (other versions: root), that which they, may their memory be blessed, said (Chullin 60b) that the Holy One, blessed be He, craves the prayers of the righteous [is] to say that His desire is that they do an act through which they will merit in front of Him and bring down from His goodness upon them; as He is One who desires to do kindness and to give from His blessing upon them, from the good of His perfection, as is written. And this is the great root to all the good that a man does in this world - that his reward from God [is because] he fulfills His desire, in that He wants the good of the creatures.