Some psalms are quite good. I agree. But still does not tell me which laws in the OT you think we should follow.
The are several different Hebrew words that can be translated as law. Fulfilment of law relates to torah, which means instructions or teaching. Teaching is fulfilled when then student attains knowledge. Following, in this sense, involves interpreting the language that flows from the original idea, which in this case is expressed by the original verse of my argument:
For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
Matthew 5:18
More context for this can be found in the other verses of Psalm 35 and the verses which relate to the entanglement of the net:
Then went the Pharisees, and took counsel how they might entangle him in [his] talk.
And they sent out unto him their disciples with the Herodians, saying, Master, we know that thou art true, and teachest the way of God in truth, neither carest thou for any [man]: for thou regardest not the person of men.
Tell us therefore, What thinkest thou? Is it lawful to give tribute unto Caesar, or not?
But Jesus perceived their wickedness, and said, Why tempt ye me, [ye] hypocrites?
Shew me the tribute money. And they brought unto him a penny.
And he saith unto them, Whose [is] this image and superscription?
They say unto him, Caesar's. Then saith he unto them, Render therefore unto Caesar the things which are Caesar's; and unto God the things that are God's.
Matthew 22:15-21