Justification, say Lutherans, is the article by which the church stands or falls. But if justification is the prime article of the faith then the incarnation is the foundation on which justification rests.
Justification by faith, the declaration of God that sinners are righteous by virtue of Christ, is meaningless without the Incarnation. Without a solid grounding in incarnational theology, a false view of justification, becomes a free pass for all sorts of mischief. Justificaton is distorted to mean that God says yes to everything and that the central truth of the Christian religion is permission. God becomes a kind old grandpa who is unable to say no to anything. This sort of distortion is central to much of liberal protestantism.
The cure for this is not to push the Law in after the Gospel as some sort of protective fence around the gospel (Yes, you are forigven but...) but it is the Incarnation. Justification is not a free floating principle untethered to any other items in theology. Justification is the chief article but not the only article. Justification by fiath is attached to the Incarnation, to the Gos become flesh in Jesus. The Incarnation grounds justification in a specific act, a specific human being, a specific history and a God who justifies in specific ways.
The Incarnation ties justification to the history of the Old Testament people who produced Mary who concieved by the Holy Spirit and gave birth to the God-man. The Incarnation ties justification to a creator God who acts through the creation he made and who inhabits the world of flesh and blood and is unashamed to make human flesh his own. The Incarnation ties justification to a real sense of the outrage of sin and the awful punishment of God's wrath heaped out in stern measure upon the man Jesus. The incarnation locates justification within the the credal Trinitarian reality of God who justifies and sanctifies through earthly created means. The Incarnation places justification in the context of the church, the office of the ministry, the sacraments.