In the future, wherever the righteous would be found holiness would be present. This is the meaning of והתהלכתי בתוככם. At that time My glory will be manifest universally, not only within the confines of the Temple. This is the time of which Isaiah 66, 1-2 said “The heaven is My throne, and the earth My footstool.”
והייתי לכם לאלוקים, I will be a special God, yours alone. You will not have recourse to any other “leader,” any intermediary who will have an input into shaping your destiny. This is why your eternal existence will not again be threatened. This is the true significance of being בצלמי ובדמותי, “in My image (and in My form.”), meaning as it had been God’s original intention. This intention had been briefly realised again at the revelation at Mount Sinai, only to have again been aborted when the golden calf was made and the people danced around it. When God said in Exodus 6,7 “I will take you to be My people and to be your God, He had meant the restoration of man’s original perfection as he had been when first created, becoming the gift of the Jewish people at Mount Sinai.
On the other hand, Deuteronomy 29,12 when God also speaks of the result of the covenant being that He will be the God of the Jewish people, He did not refer to such lofty ideals at that time. At that point the Torah was satisfied with ensuring the uninterrupted function of the Tabernacle as the home of the Shechinah on earth. This was the reduced objective we had heard about in Exodus 29,45 when God spoke about making His residence among the Jewish people in that Tabernacle, not wherever they would be in areas beyond the Tabernacle. God would indeed be the Jewish people’s God, with all that this entails in terms of His personal providence, but He would not be described as dwelling “among” them, or “within” them, depending on how we want to understand the word בתוכם. However, we would be His people, if all our efforts would be designed to carry out God’s will to the extent that He had revealed it to us. After all, every people does no less than this for its king of flesh and blood.