Reformed Bob - Let’s look at the passage in a fuller content
Isa 8:13 Sanctify the Lord of hosts himself: and let him be your fear, and let him be your dread.
Isa 8:14 And he shall be a sanctification to you. But for a stone of stumbling, and for a rock of offence to the two houses of Israel, for a snare and a ruin to the inhabitants of Jerusalem.
Isa 8:15 And very many of them shall stumble and fall, and shall be broken in pieces, and shall be snared, and taken.
Isa 8:16 Bind up the testimony, seal the law among my disciples.
Isa 8:17 And I will wait for the Lord, who hath hid his face from the house of Jacob, and I will look for him.
Isa 8:18 Behold I and my children, whom the Lord hath given me for a sign, and for a wonder in Israel from the Lord of hosts, who dwelleth in mount Sion.
Isa 8:19 And when they shall say to you: Seek of pythons, and of diviners, who mutter in their enchantments: should not the people seek of their God, for the living of the dead?
Isa 8:20 To the law rather, and to the testimony. And if they speak not according to this word, they shall not have the morning light.
Isa 8:21 And they shall pass by it, they shall fall, and be hungry: and when they shall be hungry, they will be angry, and curse their king, and their God, and look upwards.
Isa 8:22 And they shall look to the earth, and behold trouble and darkness, weakness and distress, and a mist following them, and they cannot fly away from their distress. (DRB)
Now note in verse 16 the two words which you have previously noted, testimony and law, and let’s look closer at them.
Testimony
te‛ûdâh
teh-oo-daw’
From H5749; attestation, that is, a precept, usage: - testimony.
from
‛ûd
ood
A primitive root; to duplicate or repeat; by implication to protest, testify (as by reiteration); intensively to encompass, restore (as a sort of reduplication): - admonish, charge, earnestly, lift up, protest, call (take) to record, relieve, rob, solemnly, stand upright, testify, give warning, (bear, call to, give, take to) witness.
hence for testify the implication is spoken language, this does not necessatate any book of scripture, but rather seems to imply something outside of scripture that bears witness to the Law.
Law
tôrâh tôrâh
to-raw’, to-raw’
From H3384; a precept or statute, especially the Decalogue or Pentateuch: - law.
from
yârâh yârâ’
yaw-raw’, yaw-raw’
A primitive root; properly to flow as water (that is, to rain); transitively to lay or throw (especially an arrow, that is, to shoot); figuratively to point out (as if by aiming the finger), to teach: - (+) archer, cast, direct, inform, instruct, lay, shew, shoot, teach (-er, -ing), through.
this holds the same conclusion, the diffrence is that testimony is infromal while law is formal, and the bible cannot be both formal and informal at the same time. Further the testimony and law are sealed among the disciples.
sealed
châtham
khaw-tham’
A primitive root; to close up; especially to seal: - make an end, mark, seal (up), stop.
…among the…
disciples
limmûd limmûd
lim-mood’, lim-mood’
From H3925; instructed: - accustomed, disciple, learned, taught, used.
from
lâmad
law-mad’
A primitive root; properly to goad, that is, (by implication) to teach (the rod being an Oriental incentive): - [un-] accustomed, X diligently, expert, instruct, learn, skilful, teach (-er, -ing).
the testimony and law properly belong to the disciples, that is to those whom God has taught.
as to verse 20 it is a warning to those mentioned in the preceeding verses. The prophet and his disciples are to be “signs” (v18)…
signs
'ôth
oth
Probably from H225 (in the sense of appearing); a signal (literally or figuratively), as a flag, beacon, monument, omen, prodigy, evidence, etc.: - mark, miracle, (en-) sign, token.
from
'ûth
ooth
A primitive root; properly to come, that is, (impliedly) to assent: - consent.
…they are to be a beacon of light in the world of darkness, a city set upon a hill, and what may we ask is the purpose of this sign but to perserve the testimony and law, tradition and scripture, so that the measure of the truth might be known. Why is this necessary? The Prophet also tells us that…
Isa 8:15 And very many of them shall stumble and fall, and shall be broken in pieces, and shall be snared, and taken. (DRB)
So, my friend, rather than seeing a support for SS here I see a strong argument in favor of the Catholic view of scripture, a warning against dividing the body of Christ, and a prophesy of the protestant refermation.