How Do I Know Christ Is God?
Because scripture affirms it: A list of Scripture texts which attest to the deity of Jesus Christ (The Reformed Reader).
Why Does It Matter to Me?
If he weren’t God, he could not be my Redeemer: Why must the Redeemer be truly God? (New City Catechism)
Does This Mean God Died on the Cross?
No. “It’s the God-man Who dies, but death is something that is experienced only by the human nature, because the divine nature isn’t capable of experiencing death” (R. C. Sproul at Ligonier Ministries Blog).