I wouldn’t agree with this either…the Old Law can be thought of as a set of marriage vows…a pre-figuring (or type) of the Church as the bride of Christ. You don’t make marriage vows out of fear, but rather love for your spouse.
Salvation history is a process by which God progressively revealed Himself to mankind. The ultimate revelation was Christ, and by Christ’s work on the cross, the Holy Spirit is now able to indwell, guide, transform and influence us in a different and better way than the methods illustrated in the Old Testament. Based on Israel’s history of repeatedly failing, repenting, and then failing again, it is evident that the way of grand miracles didn’t really make a lasting impression.
The need for miracles ultimately gets twisted into some pursuit of personal gain, wealth, etc. Even Christ talks about this, and I believe other Scripture (such as in Revelation) make it clear that mankind will turn its back on God even in the face of undeniable miracles. What’s necessary is a true transformation of heart enabled by the Holy Spirit.
Also, I believe there is a statement about Christ fulfilling or closing the age of public revelation in the Catechism, but my online search engine is not working for the Catechism right now.
Finally, I don’t believe that God has changed anything regarding the way he views sin, or the consequences of sin. By His Grace, we now have more ways to deal with and erase the spiritual consequences of sin (ie, the loss of everlasting life), but there are real, physical consequences that remain just as they were present in ancient history.