Is justification part of the gospel?
Justification is a legal pronouncement made by God in the present, prior to the day of judgement, declaring sinners to be not guilty.
And therefore sinners are acquitted, God pardoning all their sins and reckoning them to be righteous in his sight, on the basis of Christ, their representative and substitute, whose righteousness in life and death is put to their account when in self-despairing trust they look to him alone for salvation.