Here are a few excellent and clear Reformation statements on justification from the Formula of Concord (Epitome), article III:
We believe, teach, and confess what our righteousness before God is this: God forgives our sins out of pure grace, without any work, merit, or worthiness of ours preceding, present, or following. He presents and credits to us the righteousness of Christ’s obedience [Rom. 5:17-19]. Because of this righteousness, we are received into grace by God and regarded as righteous.
We believe, teach, and confess that faith alone is the instrument through which we lay hold of Christ. So in Christ we lay hold of that righteousness that benefits us before God [Rom. 1:17], for whose sake this faith is credited to us for righteousness. [Rom. 4:5).
Or, in the longer form of the Formula of Concord (Solid Declaration), here’s the corresponding statement:
“We unanimously believe, teach, and confess the following about the righteousness of faith before God, in accordance with the comprehensive summary of our faith and confession presented above. A poor sinful person is justified before God, that is, absolved and declared free and exempt from all his sins and from the sentence of well-deserved condemnation, and is adopted into sonship and inheritance of eternal life, without any merit or worth of his own. This happens without any preceding, present, or subsequent works, out of pure grace, because of the sole merit, complete obedience, bitter suffering, death, and resurrection of our Lord Christ alone. His obedience is credited to us for righteousness.”
“These treasures are brought to us by the Holy Spirit in the promise of the Holy Gospel. Faith alone is the only means through which we lay hold on, accept, apply, and take them for ourselves. This faith is God’s gift [Eph. 2:8-9], by which we truly learn to know Christ, our Redeemer, in the Word of the Gospel, and trust in Him. We trust that for the sake of his obedience alone we have the forgiveness of sins by grace, are regarded as godly and righteous by God the Father, and are eternally saved” (FC, Solid Declaration, Article III).
You can find these statements in the Formula of Concord (Epitome and Solid Declaration) in Concordia: The Lutheran Confessions.