The torah has these two Posukim right next to each other: Dovarim 4:2 has:
לא תספו על הדבר אשר אנכי מצוה אתכם ולא תגרעו ממנו לשמור את מצות ה׳ אלקיכם …
And 4:4 has:
ואתם הדבקים בה׳ אלקיכם חיים כלכם היום
What is the connection?
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The Sipurno connects the Pesukim as follows:
Don't subtract- don't think that when the reason for the issur goes away that you can do the issur (like Shlomo haMelech)
Your eyes see what Hashem did concerning baal peor- the original plan of those that followed baal peor was only for z'nus. They rationalized that z'nus is only assure because it may lead to avodah zara, that won't happen to us.
Everyone that went after baal peor- to be mezane, Hashem destroyed. Not one of them was able to guard himself.
But you who clung to Hashem are all alive today- You used your chochmah to guard from avoda zara (by not rationalizing the mitzva)
Reb Bunim from Psheischa answers that if you look in the world you will see the people empty of Torah, (that is those who do not study - that means they are not 'דבקים בה) are the ones who have added to the Torah. They have extra Chumros to show the world that they are holy. It is those that study, who live the regular life, who do not need to come on to additional Chumros to prove to the world their holiness. Hence he says one Posuk is placed next to the other to illustrate this point.