Why did God create a new covenant? Why did God create a new covenant?  It seems as if he had a covenant set in place in the Old Testament and provided a means for Israel to follow the covenant and offer sacrifices to atone for their sins.  Why did he create a new covenant in the New Testament which is the basis of Christianity?  Did mankind or God change in a way that a new covenant needed to be set up?
If God had created Christianity first, people would not have known their need for a Saviour. &quot;What do we need to be saved from?
So God first sets up a do-it-yourself religion; by which I mean that if the Jews followed all the laws they could save themselves earning their right to heaven.
That didn't work. Worse, some people became more interested in the laws than the purpose of the laws:

Matthew 23:23-24
“Woe to you, teachers of the law and Pharisees, you hypocrites! You give a tenth of your spices—mint, dill and cummin. But you have neglected the more important matters of the law—justice, mercy and faithfulness. You should have practiced the latter, without neglecting the former.
You blind guides! You strain out a gnat but swallow a camel.

See also: a brief summary of how salvation works.
But now people could at least compare their standards to God's and realise the gap between themselves and God:

Romans 3:23
for all have sinned and fall short of the glory of God

If you want to read more about this, the book of Hebrews explains more about how Judaism (and particularly the law) was a shadow of the forthcoming revelation. For example, the animal sacrifices in Judaism teach us that a sacrifice is required for the forgiveness of sins. This is how we can understand passages like this:

Hebrews 9:23-28
It was necessary, then, for the copies of the heavenly things to be purified with these sacrifices, but the heavenly things themselves with better sacrifices than these. For Christ did not enter a sanctuary made with human hands that was only a copy of the true one; he entered heaven itself, now to appear for us in God’s presence.
Nor did he enter heaven to offer himself again and again, the way the high priest enters the Most Holy Place every year with blood that is not his own. Otherwise Christ would have had to suffer many times since the creation of the world. But he has appeared once for all at the culmination of the ages to do away with sin by the sacrifice of himself. Just as people are destined to die once, and after that to face judgment, so Christ was sacrificed once to take away the sins of many; and he will appear a second time, not to bear sin, but to bring salvation to those who are waiting for him.