In Jesus Christ, God himself came to earth. He is God's last Word. By listening to him, all men of all times can know who God is and what is necessary for their salvation.
With the Gospel of Jesus Christ, the Revelation of God is perfect and complete. To make it comprehensible to us, the Holy Spirit leads us ever deeper into the truth. God's light breaks so forcefully into the lives of many individuals that they "see the heavens opened" (Acts 7:56). That is how the great place of pilgrimage such as Guadalupe in Mexico or Lourdes in France came about. The "private revelations" of visionaries cannot improve on the Gospel of Jesus Christ. No one is obliged to believe in them. But they can help us understand the Gospel better. Their authenticity is tested by the Church.