Yes I know that scripture, but how was the old covenant found with fault.
It was not the Psalms, and prophetic books, it was because of the mosaic laws that could not forgive and save people through animal sacrifices. The Lord came to give His one time perfect sacrifice for remission of sins.
Hold on, lets stop right here for a minute, man has always been under law from day one, we had what some call the patriarchal law, some claim this law was the law before the mosaic law, but think for a minute...
In the exodus before ever reaching Sinai Moses gave the people the command to keep the passover, was Moses forcing a situation of spiritual adultery? having the Jews commit spiritual adultery keeping two laws?, at what point were those Jews told not to keep the patriarchal law and to keep the law given at Sinai?, they weren't.
The Law Paul and our Lord referred to was the Law before Christ otherwise Moses caused the Jews to commit spiritual adultery keeping two laws.
Now lets look at what our Lord taught when Matthew had a feast on a day that the Jews fasted, Jesus gave three analogy's to deal with it the first the mourning of the children of the bridechamber:
Matthew 9:14-15 (KJV)
14 Then came to him the disciples of John, saying, Why do we and the Pharisees fast oft, but thy disciples fast not?
15 And Jesus said unto them,
Can the children of the bridechamber mourn, as long as the bridegroom is with them? but the days will come, when the bridegroom shall be taken from them, and then shall they fast.
the second, the new patch on old cloth:
Matthew 9:16 (KJV)
16 No man putteth a piece of new cloth unto an old garment, for that which is put in to fill it up taketh from the garment, and the rent is made worse.
the third new wine in old wineskin:
Matthew 9:17 (KJV)
17 Neither do men put new wine into old bottles: else the bottles break, and the wine runneth out, and the bottles perish: but they put new wine into new bottles, and both are preserved.
These three examples are the Lord teaching while He is yet with us, there is no reason to mourn, once he is gone they then will be saddened and have reason to fast, the New Law that the Christ brings like a new patch cannot be used to patch the old law (patriarch/mosaic law they were one, no spiritual adultery introduced by Moses). If the Christ put the New Law in the Old Law, like Old wineskin would burst with new wine the Old Law could not contain it...
This is why a new High Priest was needed, and with a new High Priest, was of necessity a new law...
Now if we try to obey the Old law (old testament, patriarchal/Mosaic) , and the New law (new testament, Law of Christ) we have spiritual adultery, to play instrumental music during worship, or any other form of worship used under the old law (Patriarch/Mosaic) that was not brought forward by Christ and his Holy Spirit guided Apostles is spiritual adultery...
We are told to "sing", now produce the command in the new law that says we can play mechanical musical instruments.