At the beginning of our Parashah, we are told of Ya'akov's famous ladder dream at Beit-El, wherein God promises that he will give him the Land, many descendants, that he will be a blessing to all of humanity - and that He will protect and guard Ya'akov on his journey to Haran until he returns to the Land and realizes the fulfillment of all of these promises.
When Ya'akov awoke (the second time - look carefully at B'resheet 28:16-18) in the morning, he consecrated an altar and made the following vow:
If God will be with me, and will keep me in this way that I go, and will give me bread to eat and clothing to wear and I come again to my father's house in peace; Hashem will be my God, and this stone, which I have set up for a pillar, will be God's house; and of all that You give me I will surely give one tenth to You. (Beresheet 28:20-22)
There are three difficulties inherent in this statement - and one which is external to it:
ANALYZING THE TEXT: FIVE QUESTIONS
PROBLEM #1: "NEDER AL T'NAI"
The conditional vow -neder al t'nai is odd for several reasons:
If the condition (God watching over Ya'akov) is a mirror of God's promise to him in the dream, why is Ya'akov phrasing it conditionally - "if God will be with me..." - isn't he fully confident that God will fulfill His promise?
On the other hand, if Ya'akov's condition is somehow different than God's promise - why is Ya'akov "setting the terms" for God? Isn't that inappropriate?
In any case, the condition seems unnecessary - if God doesn't help Ya'akov return to the Land, he won't be in a position to fulfill his vow. Ya'akov could have made an unconditional vow - and then, if God saw him safely back to the Land, he would fulfill it. If not, he would either be "stuck" outside of the Land, or dead; in either case absolved of his vow.
Ramban (v. 20) suggests that the conditional word im (if) is sometimes used (as in God's own words to Ya'akov in the dream - v. 15 - see also Sh'mot 22:24) as when. Here too, he suggests that Ya'akov is not making a conditional vow, rather a "delayed" vow -neder l'achar z'man - meaning, when these things (which God has promised and which I am confident will come to pass) happen, I will... Although there are other examples of this usage, it is not the simplest way to read the text.
PROBLEM #2: HOW MUCH IS "VOW"?
In Ya'akov's statement, where does the condition end and where does the vow begin? The biggest question relates to the phrase Hashem will be my God - is this the end of the condition (as Sa'adiah, Rashi, Rashbam and Hizkuni understand) or is it the beginning of the vow/commitment (Radak, Ramban)? Either reading is difficult, as follows:
If it is the end of the condition, how should it be understood? What must God do to fulfill His end of the bargain? If it means that God should be with Ya'akov (whatever that may mean - see Yehoshua [Joshua] 3:7), isn't this a restatement of the first phrase in the condition?
If it is the beginning of the vow/commitment, what does it mean? What is Ya'akov committing to do in this phrase?
PROBLEM #3: MA'ASER
The final phrase of the vow seems a bit odd - after committing to have a special relationship with God, including (apparently) to worship Him at this spot, the climax of his statement - ...and of all that You give me I will surely give one tenth to You seems incongruous. What is the import of this commitment?
There is one external difficulty:
PROBLEM #4: WHEN IS THE VOW FULFILLED?
Why was Ya'akov never called on this vow? Even though he returned to the Land, he didn't go directly to Beit-El for worship. Indeed, Rashi explains God's beckoning of Ya'akov to return to the Land:
...I am the God of Beit - El, where you anointed a pillar and made a vow to me. Now leave this land at once and return to the land of your birth. (31:13),
in this light:
and made a vow to me: - and now you must fulfill it (Rashi ibid. - see also Ramban ibid).
Rashi even sees Ya'akov's delay in fulfilling his vow as the cause for the Dina tragedy (see Rashi 35:1). In spite of this approach, there is no mention in the text of any failing on Ya'akov's part regarding his obvious delay in returning to Beit-El.
Examining one further difficulty in the text will help us understand Ya'akov's vow:
PROBLEM #5: TOLEH B'DA'AT AHERIM
In the penultimate phrase, Ya'akov states: ...and this stone, which I have set up for a pillar, will be God's house.... Although the commentaries understand some form of commitment on Ya'akov's part (e.g. to construct a sanctuary there [Radak], to worship there [Rashi]), the text is enigmatic. The simplest reading of this phrase is that this place (Beit-El) will be a house of God - but that is, of course, something which is out of Ya'akov's control. Whether the world recognizes the special nature of that location and, as a result, comes there to worship, is not something Ya'akov can guarantee - at best, he can endeavor to publicize the place and hope to attract worshippers. How can this be a vow, considering that its fulfillment is dependent on others (toleh b'da'at acherim)?
Returning to an earlier question, what is the significance of the commitment to tithe (the last clause of Ya'akov's vow)?
YITZCHAK'S FINAL BLESSING TO YA'AKOV:
BE LIKE AVRAHAM
Just before leaving his parents (and experiencing the vision which led to this vow), Ya'akov received one last blessing from his father - and this one was given with full knowledge of the recipient:
...May God Almighty bless you and make you fruitful and numerous, that you may become a company of peoples. May He give to you the blessing of Avraham, to you and to your offspring with you, so that you may take possession of the land where you now live as an alien, [the land] that God gave to Avraham. (28:3-4)
Ya'akov was blessed that he should be like his paternal grandfather, Avraham. One of the central features of Avraham's greatness was the recognition on the part of the people around him - including kings - of his special relationship with God. And that is exactly where tithing comes into the picture.
The one explicit instance of tithing found before Ya'akov was that of Avraham (Beresheet 14:17-20). Subsequent to his defeat of the four mighty kings, Avraham encountered the king of S'dom in the presence of MalkiZedeck , a priest of the Most High God. MalkiZedeck blessed him and verbally affirmed Avraham's special relationship with God (as evidenced by his military and political power). In response, Avraham gave MalkiZedeck a tenth of his goods. This was, then, the proper reaction to public recognition of one's special relationship with God. Whereas pagan belief held that a person might be favored by the gods as a matter of fate or caprice, the approach of the Torah - which is consistenly stressed and repeated - is that God's selection of an individual for blessing is a direct result of that person's saintly behavior (see e.g. Beresheet 6:9 and 18:18-19). Once someone is publicly recognized as being blessed by God, it is a supreme act of responsibility toward achieving the goal of publicizing God's Name (the Avrahamic mission) to demonstrate that His favors are bestowed upon the righteous. By tithing at that point, the righteous person shows that his special relationship with God is justified - and is accessible to other. Ya'akov knew that when he would be recognized by leaders as having a special relationship with God - that would be the point at which he would tithe.
REEVALUATING THE VOW
Now, let's look at the vow again and divide it a bit differently:
If God will be with me, and will keep me in this way that I go, and will give me bread to eat and clothing to wear and I come again to my father's house in peace; Hashem will be my God, and this stone, which I have set up for a pillar, will be God's house; THEN all that You give me I will surely give one tenth to You."
Ya'akov is vowing that when the rest of the world recognizes his special relationship with God (YHVH will be my God), he will give tithes, as did his grandfather when he was recognized as being blessed by God. This recognition would come to pass, in Ya'akov's case, by God protecting and sustaining him in exile and bringing him back home. There is, however, more to the story. Once Ya'akov becomes recognized by leaders and their people as blessed by God, it follows that any site where he worshipped would become a place of prayer and worship for others. After all, imagine how we would flock to the original Luz/Beit-El if we could unqualifiably identify the location of Ya'akov's dream - and none of us ever met Ya'akov in the flesh! How much more so would someone who saw Ya'akov and recognized his special qualities want to go back to that pillar and worship there. Ya'akov is stipulating that even if God protects him, it will only be of value to the rest of the world once they recognize this and act upon that recognition.
At that point, his tithing will make the necessary statement of commitment to all of those values which it is his job to publicize - because his position will afford him that opportunity.
We can now answer all of our questions:
Ya'akov's condition is not merely a mirror of God's promise - it takes the promise one step further. If God's protection leads to Ya'akov's public recognition as a recipient of God's blessing, then he will demonstrate the propriety of that selection by tithing.
The condition ends before the last phrase. The only commitment is found in the final phrase - to tithe.
The commitment to tithe is not so incongruous - since it is the only commitment made here. In addition, its significance is understood against the backdrop of Avraham's tithing to MalkiZedeck.
Ya'akov was never called on this vow because he never vowed to go back to Beit El (read Beresheet 31:13 and 35:1 carefully) - rather, to tithe.
Beit-El becoming a place of worship was not the commitment - it was the final condition which would commit Ya'akov to follow Avraham's model and to give a tenth of everything with which God blessed him.