God's Call To Isaiah and To Each of His Servants (Isaiah 58:1).
“Cry aloud, spare not,
Lift up your voice like a trumpet,
And declare to my people their transgressions,
And to the house of Jacob their sins.”
God calls on Isaiah, and on each of His messengers, to act as a town-crier in declaring openly to His people their transgressions and sins without fear or favour. They are to speak with the voice of a trumpet as God did at Sinai (Exodus 19:16). This is the God of Sinai coming to speak to His people again and call them back to the covenant. They are to bellow their message out as over a loudspeaker, and expose their rebellion and sinfulness. They are not to spare their listeners. The message is too important for that.
The basic idea behind ‘transgressions' is rebellion. Their hearers are rebelling against the Sinai covenant. They need to be aware that their behaviour demonstrates that they are rebels against God and rebels against that covenant. The word for sin means to miss the goal, to fail to do what is right. They are missing out on their covenant responsibilities.
‘The house of Jacob.' ‘Jacob' is often used when the bad side is being brought out. It is the pre-transformation name. But it is also the name of the one who was chosen from birth in contrast with his brother Esau, and the name used because Isaiah has dropped the use of the name Israel once the Servant was established as ‘Israel'.
The same message came later to Ezekiel when he was warned that it he did not seek to turn the sinner from his way, he himself would be blood-guilty (Ezekiel 33:8). And it is equally true today.