It's one of the greatest lines in science fiction: "I am altering the deal. Pray I don't alter it any further." Few of us are as evil as Darth Vader, but we've all had times we thought it was time to alter the deal and renegotiate. Things just didn't go the way we thought they should have, and so we decided to say, "Hang on a minute. If this is how this will really work, we need to change a few things." It could happen on the job, in a friendship, in a relationship, or even in a church.
In some ways, I think that's how some people view the change between the testaments. God made a covenant with His people through Moses, the agreement went south, and the terms changed. The new covenant came through the sacrifice of Jesus in his death, burial, and resurrection. I can see where these people are coming from, honestly. It can look like someone in the course of the old covenant decided it wasn't working out and had to renegotiate the terms of their relationship with God. If we try to make that work as an analogy, it's interesting to note who wanted to renegotiate: God.
And that's what grace and love look like.
In the fullness of time, God knew it was necessary to fulfill and replace the law He had given Moses. It had done its job: the hearts of Men were now prepared to receive the final sacrifice ever to be made for the forgiveness of sins. It was time to give us Himself, the only-begotten Son of the Father. Only the blood of Jesus could fulfill the terms of the old covenant on behalf of the world. Only he could establish a new covenant, defined not by law but by grace. Those would be the new terms: salvation would come by grace through faith.
In the end, though, the purpose of the deal remains the same: so the sons of Adam and daughters of Eve could know forgiveness of sins, everlasting life, and a living God.