Exodus 19:23 New International Version (NIV)
23 Moses said to the Lord, “The people cannot come up Mount Sinai, because you yourself warned us, ‘Put limits around the mountain and set it apart as holy.’”
The people could not come to God themselves because he is completely holy. God did this to show them that he was not like an idol that could be seen and touched. Now, we get to approach God because of what Jesus did for us on the cross. Jesus opens the way for us to come to God with great joy.