By the mitzvah of Shabbos, it says here: “And you shall remember that you were a slave in Egypt and Hashem took you out from there with a mighty hand and outstretched arm, therefore Hashem your G-D commanded you to make the day of Shabbos” (Devarim, 5:15).
If inculcating this aspect of faith in Hashem is so incredibly important, then why wasn’t it written in a respectful manner in the first set of commandments, just as it wrote “that I took you out of Egypt?” That reference also alludes to their slavery, but does so in a nicer tone, to remind them in the first commandment of belief of Hashem’s oneness.
We must therefore say, that by speaking in a more respectful manner by the mitzvah of Shabbos, and not stating: “And you shall remember that you were a slave in Egypt,” it would not have had the same impact, to strengthen this particular aspect of belief in Hashem. The connection of one’s servant resting on Shabbos to us being slaves in Egypt and being redeemed by Hashem would not have been clearly articulated, and the impression would not have been a worthwhile impression, which would make enough of a difference to inculcate this lesson into our lives.Therefore, even if it is an extremely important lesson to be repeated, and it could be taught in a more respectful but more subtle manner, then it is still not worth teaching it at that time since its full impact is not there.
We see how important it is to weigh our words and be sure what comes out of our mouth is the most effective message at the present time, even if it comes at the expense of delaying and not repeating a central message that must be delivered.