If only they could fear me all of their days ...

See Devarim, 5:26

If only their hearts were with me in this way, revering me and guarding My commandments all the days, so it will be well for them and their children forever. Go and tell them, 'go back to their tents.'

This fatherly reaction, God looking at us after we recieved the Torah, where we had become purified like angels, and thinking, "wow, if only the children of Israel could stay on this level all the time," God knows what is best for us, but he wants us to learn our own lessons, and choose the good for ourselves. Why did God make man who could act with his own free will and transgress God's commands? It is as the Holy Kotsker said, that God has enough holy angels; what he really wants is holy men. And the Kotsker's talmid chaver, his soul brother, his adversary, his friend, Rav Mordechai Yosef knew that God wants us to act with love in the world, to be loving and help others, and when you act with love you cant be so holy and separate.
For instance, if you see someone's car stopped on the side of the road with a flat tire, and you want to stop and help him change the tire, you are going to have to get your hands dirty. Fasting is an ancient way of cleaning one's soul, but only if done in the right way. I heard from my Rebbe Reb Brandvine, Shlita, that the Chassidim where not big fans of fasting. At best, when you fast, you are only helping yourself, but when you eat, at least you have the strength to help others. When you fast, you are helping yourself not only to control your appetite but to do teshuvah, to return in Joy to God's law. And still, it is only for yourself. Mazal Tov. What about putting your holy arrogance aside and helping another person? So perhaps you see what Rav Mordechai Yosef, the Mei HaSHiloach, meant when he said that acting with love in this world necessitates that wont be able to keep so clean - reserved for God and removed from the world. But don't think that there is any contradiction here between the Kotsker and the Isbitser (Mei HaShiloach), a holy man will eat in a reasonable way so he has the strength to help others. A holy man will get his hands dirty and change the tire. Sitting in Yeshivah is great, if only we could all spend an hour every day and night trembling with joy over the Gemara and the holy books, but a baal chesed - a man of kindness and generosity, a man with a heart, will overcome his own nature and do for others.

"Go back to your tents." This statement is commonly understood that the celebicy practiced by the children of Israel that was needed in order to receive the Torah was no longer neccesary, and the men could, "go back to their tents," and be intimite with their wives. But it is saying more. God was saying, "Do you see the tremendous vision you had, where you were so holy that your souls went out of your bodies and witnessed visions of God to last for all generations? Take that vision and that lofty level of holiness and bring it into your tents, conduct yourselves in the bedroom as if you were standing before me. You were standing and your souls where united in divine intercourse with the Shechina. It was not a physical experience, you did not do it to satisfy a lust, but rather to unite with the source of all in a moment of fertility that will give birth to the ability of man to connect to God for all genrations hence. Now take that higher purpose and divine union, and know that I fill the whole world with My glory, I am in the bedroom no less than I am in the synagogue or at the Kotel. So conduct yourselves in a reasonable and holy way in private just as you strive to in public.

So, if I may be allowed to say it, and May God forgive me if I am wrong, the verse, "if only they could fear me all their days ... go back to your tents," means that at times you need to strive for an other worldly holiness, fasting, silence, abstinence, nullifying yourself before God. These are all found in the ways God commanded us and in the course of the Jewish year. But you were not meant to be an angel, you were born in order to struggle to be an holy man, and at times succeed. Take all your love for God, all of your desire for holiness and purity, and put it into your daily and physical life, wereby you can truly transform the physical and saturated it with kedusha and spirituality.