The deep things of God?

What are “the deep things of God” that no eye has seen in 1 Corinthians 2? How were we crucified with Christ if we’re not that old? Was Peter given the keys to the kingdom, becoming the first pope? What are your thoughts on common law marriage? How do we know we are eternally secure? My adult children are rejecting faith in Christ and rejecting me. How does God view the lives of unbelievers? Is Hebrews 6 saying I might lose my salvation if I can’t quit smoking?