How new are you? The Old Testament is the story of the continued failures of the Hebrew people with a few great kings and prophets sent to try to put them back on the right track, which inevitably fails after a generation when the Hebrews start doing even more depraved and evil things; leading to punishment, and then another prophet or king sent to bring them back. This continues until Jeremiah where Israel is destroyed, and the Old Testament ends in Malachi where Judea is threatened with absolute destruction and an incineration of all its people in ovens. Yes really.
Then Jesus comes to "separate the wheat from the chaff". The chaff is going to be incinerated. David is one of the 'good guys'. I'd rather not call him a 'good jew' because judaism did not exist at this time, in fact judaism is a younger religion than Christianity and would be better off being referred to as Talmudism. Many Hebrews trod the path of the Talmudist before the Talmud or Judaism ever existed, but the king and prophets that were sent to chastise them and lead them back to the righteousness were good guys. A large portion of the New Testament is Jesus saying 'woe unto you pharisees (those who would become the jews) and criticising them for ignoring the commandments of God and turning away from the righteous path in favour of evil.
Here is a rather unsubtle parable that explains the whole thing.
Mark 12:1-12
And he began to speak unto them by parables. A certain man planted a vineyard, and set an hedge about it, and digged a place for the winefat, and built a tower, and let it out to husbandmen, and went into a far country.
And at the season he sent to the husbandmen a servant, that he might receive from the husbandmen of the fruit of the vineyard.
And they caught him, and beat him, and sent him away empty.
And again he sent unto them another servant; and at him they cast stones, and wounded him in the head, and sent him away shamefully handled.
And again he sent another; and him they killed, and many others; beating some, and killing some.
Having yet therefore one son, his wellbeloved, he sent him also last unto them, saying, They will reverence my son.
But those husbandmen said among themselves, This is the heir; come, let us kill him, and the inheritance shall be ours.'
And they took him, and killed him, and cast him out of the vineyard.
What shall therefore the lord of the vineyard do? he will come and destroy the husbandmen, and will give the vineyard unto others.
And have ye not read this scripture; The stone which the builders rejected is become the head of the corner:
This was the Lord's doing, and it is marvellous in our eyes?
And they sought to lay hold on him, but feared the people: for they knew that he had spoken the parable against them: and they left him, and went their way.