Isaiah 55:1 becomes more revealing in its context. Indeed, we need to relate it to 55:3, but there is some more. According to some commentators (see among others D.C. Flemming, Concise Bible commentary, AMG Publishers, Chattanooga, Tenn., 1994, p. 268), this is spoken during the exile, in a period of time when many of the Jews had made life tolerable for themselves, if not even prosperous, in Babylon. And were more concerned with making their living. Whereas God's blessings are free and cannot be bought with money. In addition to this, they bring more satisfaction than all the temporary benefits, earned with hard work and money.
There is also an interesting study by K. Baltzer and P. Machinist (see Deutero-Isaiah : A commentary on Isaiah 40-55 in Hermeneia-a critical and historical commentary on the Bible, Fortress Press, Minneapolis ,2001, p. 466-467) - they parallel Isaiah 55:1-5 with Proverbs 9:1–12, where “Lady Wisdom” is inviting to her banquet:
“You that are simple, turn in here!” To those without sense she says,
(5) “Come, eat of my bread and drink of the wine I have mixed. (6) Lay
aside immaturity, and live, and walk in the way of insight.” (NRSV)
Baltzer & Machinist underline the fact that common to both Isaiah 55:1-5 and Proverbs 9:1–12 is: 1. the transferred meaning of food and 2. the lesson is that (true) life is the benefit gained from this banquet (Baltzer & Machinist, 2001, p. 467).
This parallel (Isaiah 55:1-5 and Proverbs 9:1–12) have been noticed even long before and people tried out to see how things would fit together. A commentator like Jerome (cca IV-Vth century) was saying:
Jerome, Commentary on Isaiah, 15.11:
It is very marvelous how they can buy water without money and do not
drink it but eat it. For he who came down from heaven is himself both
bread and water.… We read that he mixed wine and wisdom in his bowl,
telling all the fools of this age and the world who do not have wisdom
to drink, that we buy not only wine but also milk, which signifies the
innocence of little ones. The manner and type of this remains today in
the Eastern churches, where wine and milk are given to the newborn in
Interesting this IV/Vth century Eastern custom, to give wine and milk to the newborn in baptism - never heard of this before. This would be off topic so we should stop with it here.
If we are looking in the Jewish exegetical lineage, we find some very interesting insights.
Avodah Zarah 5b: Rabbi Yoḥanan says in the name of Rabbi Bana’a: And the term waters is referring to nothing other than the Torah, as it
is stated: “Ho, every one that thirsts, come for water” (Isaiah
It seems there is a very solid exegetical tradition that would equate water = Torah, on the basis of Isaiah 55:1. See an example of it:
Mishneh Torah on Torah study 3:9
The words of the Torah are likened unto water, even as it is said:
"Ho, everyone that thirsteth, come ye for water" (Isaiah 55:1), which is
to teach you, even as waters do not gather in steep places, but flow
by gravity and gather in a well, so are the words of the Torah, they
are not found among the high spirited nor in the heart of all haughty
but in the humble and meek spirited who embraces the dust of the feet
of the wise and removes the passions and the pleasures of the age from
his heart and does a little work daily for his living, if he happens
to be unprovided with food, and the rest of his days and his nights he
pursues the study of the Torah.
Almost the same idea in: Sukkah 52b:2; Kiddushin 30b:8; Sifrei Devarim 48:5, etc.
For wine and milk:
Ibn Ezra on Isaiah 55:1 Buy for nothing, and eat without paying. Wine and milk. Each serves both for food and drink, as medical
authorities assert. The function of the drink is to dissolve the food
and to accelerate its digestion; most beverages are believed to
contain no elements of nourishment, but in wine and milk both
properties are found, they nourish and accelerate the digestion. Wine
and milk are mentioned because the Law is compared with them.
Almost the same idea in Shir HaShirim Rabbah 1:2:8. It would be interesting to see if there are other passages in the Bible + Jewish exegesis in which the Law is compared with wine and milk.
Therefore in Isaiah 55:1, the water, wine and milk offered by God himself would be symbols of spiritual blessings, offered for free to all who might be looking out for them. If we try to sum up the symbols mentioned above, these would be: Torah, wisdom, innocence. There is an idea of gradation, indeed. The good old Commentary Critical and Explanatory on the Whole Bible would mention this.
In the end, if we take into account this idea of gradation too, the meaning could be: thorough the study of the Torah (the Law of God), through getting to know the will of God, one would gain wisdom and reach innocence.