At Mount Sinai the Jews connected with G-d. They saw the clouds, heard the thunder of the Shofar, and heard the voice of G-d speaking the commandments. Under such circumstances they had a lot of drive to follow the advice given by G-d to do the commandments.
When they left the mountain, from which they received the Torah, they left behind the connection to G-d. Without a connection to G-d it is easy to slip away from the holy commandments which we heard from G-d.
A connection between G-d and Israel was constructed. This was the Mishcan. In the Mishcan people could go to feel G-d. This could give them the drive to follow all of the Mitzvot.
The People clearly new the importance of this project. When Moshe asked them to give money and goods for the Mishcan everyone voluntarily gave. They gave so much that Moshe had to tell them to stop giving.
A Synagogue is an extension of the Mishcan. The non-observant people even call it a Temple.
When B’nai Yisrael was expelled from Israel they thought that their connection to G-d had been severed. Of course the implication is that they need not follow the Mitzvot any more. The Prophet Yechezkel told them in the name of G-d he will personally be a Mikdash Me’at – A small temple. Our rabbis have discussed at length that this Pasuk refers to Synagogues. Through the Synagogues we can get the feeling of G-d in our midst.
If you follow the train of thought of the things which I have discussed you will see that a Synagogue can be equal to the experience at Sinai. It can bring us closer to G-d and help us act correctly according to the Torah. If the Mishcan fills in for the Sinai experience and the Synagogue is in place of the Beit Hamikdash then the Synagogue can fill the void in our connection to G-d.