In Parashat Vayetzeh, Yaakov goes to Lavan's house, but prior to his arrival he meets up with Rachel. Shockingly, the Pasuk says that he kissed her and cried (29:11). How exactly are we to understand this episode? Do we not say that the Avot kept the whole Torah before it was given, and can we not assume that the righteous Yaakov would not do something so immodest as to kiss a girl he isn't married to yet - in public?
Many commentaries have offered explanations to this issue. Even if you disregard societal differences of modesty or niddah concerns, there are other possibilities. Here are a few:
Rachel was too young to arouse passion
ורחל היתה קטנה ואין לחוש לה. וזה ענין וישק יעקב לרחל
Rachel was young and so there was no concern [that she went shepherding alone], and that is the way "Jacob kissed Rachel" [was permissible].
The Seforno indicates (on 29:18) that Jacob had to work so long for Lavan so that she be old enough to marry:
בתך הקטנה. כי תוך ז' שנים יהיה עתה עת דודים ותוכל בין כך להשיא הגדולה
your younger daughter - During these seven years she would reach marriageable age and in the meanwhile [Lavan] would marry off the older daughter.
Jacob was related to her and old.
This argument bolsters the first and is usually explained concurrently. As the Seforno comments, this is why in the verse after the kiss does Jacob tell Rachel that they're related :
וישא את קולו ויבך. על שלא זכה לשאת אותה בנעוריו והיו לו לעת כזאת בני נעורים
And he raised his voice and wept - that he didn't merit to marry her in his youth for then he would have had children born to him as a young man.
כי אחי אביה הוא. להודיע שלא חטא במוסר כשנשק אותה
that he was her father's relative - to assure her that he did not act improperly by kissing her.
וכי בן רבקה הוא. הזכיר לה את רבקה אף על פי שהיתה בלתי נודעת לרחל כדי שתגיד לאביה
and that he was Rivka's son - He referred to Rivka even though she didn't know her, so that she would tell her father.
In this case, being related and the age gap permitted it in the spirit of the halacha (Shulchan Aruch Even HaEzer 21:7) that parents can kiss their young children.
Jacob kissed her head/shoulder/hand or blew her a kiss
Ramban offers this other explanation. He refers to Ibn Ezra's commentary on Jacob kissing Isaac (27:27). In both cases, the verb "kiss" is following by the preposition "to" or "towards." This could mean that he didn't actually kiss her, or that it wasn't on the lips. Ramban writes:
או הוא כדברי רבי אברהם (לעיל כז כז), כי נשיקה בלמ"ד איננה בפה, רק נשק אותה על ראשה או על כתיפה:
Or perhaps this is like R. Avraham's explanation (cf. 27:27), that kissing with a lamed means it wasn't on the lips. It was only kissing her on her head or on her shoulder.
It seems that explanation softens the potentially erotic conjuring of kissing.
There are other explanations, especially kabbalistic ones, but these are the most common peshat explanations.
The gemaroh in Kesubos daf 17 says that Rav Acha danced with the kallah on his shoulder. When the Chochomim asked if they were allowed to also? He answered - if she is like a beam in your eyes then you could do it too. But if not then certainly not. That was all only in those days when they were on a tremendously higher level then us today. Nowadays, shulchan aruch (pischei tshuva on Even Haezer 65:1) rules that we are not allowed to because nobody could say that holding the bride effects him like a wooden beam.
Tanhuma Exodus 28, says that "all kisses are of tifluth, except for the kiss of parting, the kiss of honoring and the kiss of meeting." the kiss of meeting is a permissable display of affection between close relavtives. Here, the Torah, 29.10 is telling us that Ya'acov is being reminded of Rivkah when he sees Rachel. It repeats the phrase "his mother's brother" three times in passuk 10 to emphasize he is the son of Rivkah but only to tell us of the emotional encounter - "and he raised his voice and wept." VaYishaq - "kissed" 29.11, is related to 29.10, VaYashe'qe "watered" - the Torah is emphasizing he watered Rachel with his tears!!! (without vowels, VaYishaq "kissed" is spelled the same as VaYashe'qe "watered"...)
Rabbi Shimshon R Hirsch comments that the Torah mentions a number of times, in various phrases surrounding the kiss, that Rachel was Jacob’s kin. The Torah wishes to point out that Jacob’s actions were within the context of the realization that Rachel represented the continuation of his family’s traditions and values. In addition, Jacob sensed the embodiment of his sainted mother, Rebecca’s, persona. The intense emotion engendered by these awarenesses caused Jacob to kiss Rachel. Indeed, notes Rabbi Hirsch, Jacob’s tears should be sufficient proof that his Jacob’s intentions were completely pure.
Just to add what has not yet been mentioned:
Bereishis Rabbah 70:12 likewise mentions the three types of kisses that don't come under the banner of 'tiflus' like the Midrash Tanchuma mentioned above, and adds that there is a fourth type - that of a kiss to a relative:
רַבִּי תַּנְחוּמָא אָמַר אַף נְשִׁיקָה שֶׁל קְרֵיבוּת, שֶׁנֶּאֱמַר: וַיִּשַּׁק יַעֲקֹב לְרָחֵל, שֶׁהָיְתָה קְרוֹבָתוֹ
Rabbi Tanchuma says even the kiss of relatives, as it says: "And Yaakov kissed Rachel" - since he was her relative.
The Midrash in Shemos Rabbah 5:1 adds on this point:
וְיֵשׁ אוֹמְרִים אַף נְשִׁיקָה שֶׁל קְרֵיבוּת אֵין בָּהּ גְּנַאי
And there are those who say that even a kiss of relatives is not a disgrace.
The Mishnas Rebbi Eliezer (see line 5) notes that the reason why Yaakov cried following his kiss was because he saw people whispering to each other questioning his actions and suggesting that he had introduced a sense of immorality to their environment. Therefore he immediately started crying to demonstrate that it was not a kiss of lewdness ('tiflus') or the like, but rather that of קְרֵיבוּת i.e. one of kinship.