וַיֹּ֥אמֶר יְהֹוָ֖ה אֶל־מֹשֶׁ֥ה לֵּאמֹֽר׃ דַּבֵּ֞ר אֶל־בְּנֵ֤י יִשְׂרָאֵל֙ וְאָמַרְתָּ֣ אֲלֵהֶ֔ם וְעָשׂ֨וּ לָהֶ֥ם צִיצִ֛ת עַל־כַּנְפֵ֥י בִגְדֵיהֶ֖ם לְדֹרֹתָ֑ם וְנָ֥תְנ֛וּ עַל־צִיצִ֥ת הַכָּנָ֖ף פְּתִ֥יל תְּכֵֽלֶת׃

“Hashem said to Moshe saying. Speak to the children of Israel, and tell them that they should make themselves fringes in the borders of their garments throughout their generations, and that they put on the fringe of each border a cord of blue".

See the Ohr Hachaim who asked why it says here "ויאמר ה' אל משה לאמר" while usually it says "וידבר ה' אל משה לאמר"? 

He also noted the double language of "דבר אל בני ישראל ואמרת אליהם" - "Speak to the children of Israel, and tell them" [and as the Alschich noted that אמירה denotes soft speech while דיבור denotes harsh speech. So how do they work in tandem?].  

He also asked what the meaning of the "ו" is in the word "ועשו" "AND they should make tziztis". What is the "ו" connecting to?

He also asks about the meaning of "לדרתם" - "for the generations". ALL mitzvos are for all the generations?? 

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It would appear that all mitzvos have either a hidden reason or revealed reason or both but tzitzis are different insofar as that the in the mitzva itself we have a reason, as it says "וראיתם אתו וזכרתם את כל מצוות השם" - We see the tzitzis and remember ALL the mitzvos of Hashem etc. In the Shulchan Aruch [8-20] it says that we should have kavanna when we wear our tzitzis to remember all the mitzvos. The Bach says that since the pasuk gives the reason for the mitzva it must be that having the reason in mind  is part and parcel of the mitzva. So we see that besides the מעשה מצוה there is also a fulfillment of וראיתם אותו וזכרתם - seeing and remembering all the mitzvos. 

Now we can say that when the pasuk says "דבר אל בני ישראל ואמרת אליהם ועשו" is because "דבר" which is a harsh language refers to the primary obligation to wear tzitzis because if he didn't put tzitzis on his 4 garments he nullified this mitzva and transgressed his obligation. In addition it says "ואמרת" which is a softer tone, and that relates to the lighter obligation of seeing the tzitzis and remembering all the mitzvos which is not critical and not מעכב the mitzva and thus not framed as "דיבור" but rather as "אמירה".  

According to this we can explain what it says "ויאמר ה' אל משה לאמר" and not "וידבר ה' אל משה לאמר". Despite the fact that the act of wearing tzitzis is obligatory, the foundation and bais for the mitzva is the fulfillment of "וזכרתם" - "remembering". In order to remember the Torah commanded us to wear tzitzis. Since this fundamental matter is not an absolute obligation, the Torah couches the mitzva in terms of "ויאמר" [which denotes softness]. That also explains the "ו" of "ועשו" - You must remember all the mitzvos [ויאמר] AND as a result "ועשו" you have to wear tzitzis. 

Now we can answer the question of the Alshich who asked why the psukim speak in the third person [לשון נסתר] as in "ועשו להם ציצית" and "ונתנו על ציצית" while in פסוק ל"ט it says "והיה לכם לציצית וזכרתם" [second person - לשון נוכח] and not "והיה להם לציצית"? Why the change? 

When it talks about the primary matter of remembering the pasuk speaks to us directly "וזכרתם". But when talking about the outgrowth of the fundamental issue at hand i.e. the act of wearing the tzitzis, the pasuk speaks in the third person - "ועשו להם ציצית" "ונתנו על ציצית". 

Now we can explain the command to fulfill this mitzva for all the generations "לדרתם". Tosfos in Menachos [43b] explain that tzitzis are a garment the display our servitude to the Creator. There is a qualitative difference between a temporary עבד and an eternal עבד [see Kiddushin 4a and Yevamos 70a "ואני אומר קנוי קניו עולם אינו אוכל"]. The tzitzis must be worn with the attitude that we are ETERNAL עבדים to Hashem [and not just that we have to keep the mitzvos for all the generations, because that applies to all mitzvos].

[עפ"י תורת מו"ר הגאון הגדול רבי ד"י מן זצ"ל]