If the Shema, the Jewish confession of faith to love God in Deut 6:5 was so important that devotees recited it every morning and evening each day, adding "mind" to this Greatest Commandment must be important, as the addition of Lev 19:18, to love your neighbor as yourself.
I’m assuming the change from the Hebrew feeling word for love ahab, to the action Agapao is significant as loving our neighbors as ourselves, in what we do for them, not just our feelings towards them. Is this correct?
For the record, Deut 6:5 is NOT the Shema - the word does not appear in Deut 6:5. The Shema is Deut 6:4 because that verse begins with the command to "hear".
Deut 6:5 as commonly (and correctly) translated from the Hebrew is this:
And you shall love the LORD your God with all your heart and with all your soul and with all your might/strength.
Note the order of words: heart, soul, might/strength
This text has numerous variations in translation. Here is a list:
(Rahlfs LXX textual apparatus lists some variations.) The "heart" vs "mind" difference is almost excusable as "heart" in Hebrew is often used as a metaphor for the thinking and emotional ability (as in many other languages).
In the NT, Jesus is quoted as saying
Some get quite hung-up about these differences; I do not. The important point is that which both Deut 6:5 and Jesus make - we are to love God supremely with our entire being. The various lists are merely merisms for our entire human ability and psyche.
Citing Deut. 6:5, Claude Tresmontant observed:
When we translate literally the Hebrew be-kol lebabeka as 'with all you heart,' we evidently cannot be faulted too badly. After all the Hebrew leb does mean 'heart.' Nevertheless because the 'heart' was considered by the ancient Hebrews to be the organ of the intelligence and not of affectivity, we fail to render the true meaning of the sentence when we translate leb literally. To love with all one's heart for us it to love with very great emotion and affection; understanding this command in that fashion, we are unlikely to realize that we were really commanded in this passage to love God with all our mind or intelligence. (The Hebrew Christ p. 190)
--
New Testament usage
It is interesting therefore to note how the Gospel of Matthew renders the passage from Deuteronomy when quoted by Jesus:
Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. (Matthew 22:37)
Despite being very faithful to the Hebrew structure of the passage in Deuteronomy (more-so than are Mark or Luke), the Greek of Matthew preserves meaning by adding a word not found in the original Hebrew text (although Matthew also excludes a word too). The rendering/translation of this passage is discussed by Tresmontant as well:
"[The writer] was evidently well aware of the full meaning of leb and the full range of possible translations. Accordingly, he included both of the applicable Greek words." (The Hebrew Christ p. 191).
The heart was the thinking organ. "Heart" in English does not convey that meaning, and so the sense of the word has been lost.
This is a genuine translator's dilemma--which is why it is unsurprising that different translators have handled the passage differently. Do you translate the word (heart) or the meaning (the thinking organ)?
--
Conclusion
There's no reason to question that He said "heart", and in the world in which He lived, it conveyed what we today would more appropriately render as "mind".
In writing to Greek-speaking audiences, later writers incorporated the word "mind" to preserve meaning. Mark wrote to a Greek-speaking audience, so his editorial decision to follow a point of clarity from the LXX (as already noted by Dottard) is unsurprising.
In the Gospels we have two passages:
Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind (Matthew 22:34).
ὁ δὲ Ἰησοῦς ἔφη αὐτῷ· ἀγαπήσεις Κύριον τὸν Θεόν σου ἐν ὅλῃ τῇ καρδίᾳ σου καὶ ἐν ὅλῃ τῇ ψυχῇ σου καὶ ἐν ὅλῃ τῇ διανοίᾳ σου.
And thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind, and with all thy strength: this is the first commandment (Mark 12:30).
καὶ ἀγαπήσεις Κύριον τὸν Θεόν σου ἐξ ὅλης τῆς καρδίας σου καὶ ἐξ ὅλης τῆς ψυχῆς σου καὶ ἐξ ὅλης τῆς διανοίας σου καὶ ἐξ ὅλης τῆς ἰσχύος σου. αὕτη πρώτη ἐντολή.
Following Rahlf's edition of the Septuagint and the notes in Bagster's Handy Concordance of the Septuagint (assuming I am reading the notes and preface correctly), there might have been at least two versions of the Septuagint extant at the time of the Apostles.
The Sinaiticus, Vaticanus, and Ephraemi Codices read:
And thou shalt love the Lord thy God with all thy mind, and with all thy soul, and all thy strength.
καὶ ἀγαπήσεις κύριον τὸν θεόν σου ἐξ ὅλης τῆς διανοίας σου καὶ ἐξ ὅλης τῆς ψυχῆς σου καὶ ἐξ ὅλης τῆς δυνάμεώς σου.
The Alexandrinus Codex reads:
And thou shalt love the Lord thy God with all thy heart, and with all thy soul, and all thy strength.
καὶ ἀγαπήσεις κύριον τὸν θεόν σου ἐξ ὅλης τῆς καρδίας σου καὶ ἐξ ὅλης τῆς ψυχῆς σου καὶ ἐξ ὅλης τῆς δυνάμεώς σου.
Note that the Septuagint versions also use a different Greek word for "strength" than what is in the Gospel according to Mark.
What Jesus actually said was none of these, since he spoke Aramaic or maybe Hebrew and not Greek. But the word "mind", not "heart" is possibly what appeared in the majority of Septuagint versions, from one or more of which the Evangelists always almost quoted when writing the Gospels.
The following essentially answers the question. The word translated heart לבב in the Shema means the insides and includes mind.
Figure 1. Words νοῦς translates in the Septuagint (LXX) (Generated by Logos Bible Software).
Figure 2. Words διανοίας translates in the LXX (Generated by Logos Bible Software).
לֵבָב ... ψ 104:15 inner man, mind, will, heart... -- Brown, F., Driver, S. R., & Briggs, C. A. (1977). In Enhanced Brown-Driver-Briggs Hebrew and English Lexicon (p. 523). Clarendon Press.
