The music I've linked to below is of a psalter passage that may seem at first glance to be a slightly unusual reflection for worship. (Here is the full psalm in more modern wording.) "Testify against" here seems to have the sense of admonish or exhort, since in this passage God is not chastising but reminding; in the subsequent passage (verses 16-22), in words that sound very much like Jesus speaking to the scribes and Pharisees, He will send a stern warning to those who pose as His but whose actions say that they are not.
Why does this passage sung here from the psalter speak to me? Because it reminds me not just that my God is God, and is mine, but that what He asks of me is not performance, but relationship. Not ritual, or striving, but gratitude.
performed on SoundCloud by Niall Maclennan (Niallags)
My people Isr'el hear, speak will I from on high,
Against thee I will testify; God, ev'n thy God, am I.
I for thy sacrifice no blame will on thee lay,
Nor for burnt-off 'rings, which to Me thou offer'dst ev'ry day.
I'll take no calf nor goats from house or fold of thine:
For beasts of forests, cattle all on thousand hills, are Mine.
The fowls on mountains high are all to Me well known;
Wild beasts which in the fields do lie, ev'n they are all Mine own.
Then, if I hungry were, I would not tell it thee;
Because the world, and fullness all thereof, belongs to Me.
Will I eat flesh of bulls? or goats' blood drink will I?
Thanks offer thou to God, and pay thy vows to the most High.
And call upon Me when in trouble thou shalt be;
I will deliver thee, and thou My name shalt glorify.
(Capitalization added to pronouns that refer to God)