How is Jesus God's final word? (Catholic Perspective)

Question

The Youth Catechism of the Catholic Church says plainly (emphasis added):

In Jesus Christ, God himself came to earth. He is God's last Word.

Indeed, Hebrews 1:1-2 says,

God, having spoken earlier at many times and in many ways through the Prophets, spoke to us in these last days by the Son, who he established heir over all things and through whom he made the ages.

From a Catholic perspective, what does it mean that Jesus is God's last word? Has God spoken to man in the time since Jesus' teaching? If so, by what method has he done so? If Jesus is God's last word why is that so? For what reason Jesus is God's last word and not eq. Muhammad?

Answer 1

That section of the Youth Catechism for the Catholic Church explains itself quite clearly.

The quote you reference is the first line of the answer to the question:

With Jesus Christ, has everything been said, or does revelation continue even after him?

Including your quote, the answer continues on:

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.

So it says, in the first paragraph, that the Gospel (good news) of Jesus Christ is Universal in scope - valid for "all men of all times" and Ultimate in purpose - they "can know who God is and what is necessary for their salvation." It goes on to imply, in the second paragraph, that it is possible to receive additional "private revelations", but they will only be judged authentic if they are consistent (and don't go 'beyond') the 'final' (in terms of completeness or what is required - "perfect and complete" - not final in a temporal sense) revelation that God has given us in Christ. It is the Church that can make the determination of whether "private revelations" are in accord or contradictory to the 'final word'.

It then further explains the important concept of:

Incarnation - from the latin caro, carnis=flesh, "becoming flesh". God's act of becoming man in Jesus Christ. This is the foundation of Christian faith and of hope for the redemption of mankind (emphasis added)

i.e. God speaks to us most clearly (and 'finally' in the sense given before) by becoming one of us, and yet showing his Holy nature within the context of human flesh - "God himself came to earth".

It further references (part of) the scripture that most clearly delineates this doctrine:

1 In many and various ways God spoke of old to our fathers by the prophets; 2 but in these last days he has spoken to us by a Son - Hebrews 1:1-2a RSV

The quote stops there, but it is well worth examining the complete discourse on the topic at the beginning of the epistle to the Hebrews which actually continues well into the third chapter: Heb 1:1-3:6 RSV, with further illumination on the superiority of Christ over all servants of God later in the epistle as well.

Finally, it includes illuminating quotes from the Catholic luminaries Blaise Pascal:

Apart from Jesus Christ, we do not know what God, life, death, and we ourselves are

and Mother Teresa of Calcutta:

I have no imagination. I cannot picture God the Father. All that I can see is Jesus.

These quotes are in line with the Bible's teaching from 1 John 4:12-15 & 20 RSV:

12 No man has ever seen God; if we love one another, God abides in us and his love is perfected in us. 13 By this we know that we abide in him and he in us, because he has given us of his own Spirit. 14 And we have seen and testify that the Father has sent his Son as the Savior of the world. 15 Whoever confesses that Jesus is the Son of God, God abides in him, and he in God... 20 If any one says, "I love God," and hates his brother, he is a liar; for he who does not love his brother whom he has seen, cannot love God whom he has not seen.

Additionally, not mentioned in that particular section, is the concept of Jesus as the 'logos' i.e. the eternal word of God (cf. John 1). In this sense, Jesus is the first and last word of God and every word in between! For example:

10 The prophets who prophesied of the grace that was to be yours searched and inquired about this salvation; 11 they inquired what person or time was indicated by the Spirit of Christ within them when predicting the sufferings of Christ and the subsequent glory. - 1 Peter 1:10-11 RSV (emphasis added)

Summary: Jesus is God's 'last word' in the sense that through Him and only Him can we truly know God - any others that have or teach a contradictory revelation are respectively deceived or deceivers.

Answer 2

I think a lot of Muslims think the Jesus is dead like Muhammad is. If that were the case, then Christians and Catholics in particular would have a hard time justifying their own births.

Catholics (who believe in Sacraments - visible signs of God's invisible reality) believe that God still does things on Earth and leaves his mark on our souls, just like an author would leave a mark upon a book. He literally write the law of nature into our hearts at birth and literally etches His initials into us like a lover would upon a tree stump at baptism.

But, what the Catechism makes clear is that the Bible is the completion of Public Revelation:

"The Christian economy, therefore, since it is the new and definitive Covenant, will never pass away; and no new public revelation is to be expected before the glorious manifestation of our Lord Jesus Christ." Yet even if Revelation is already complete, it has not been made completely explicit; it remains for Christian faith gradually to grasp its full significance over the course of the centuries.

CCC 66 - quoting Dei Verbum in reference to 1 Timothy and Titus

And, by "no new Public Revelation" it means, there's nothing extra anyone needs to know to get to know Christ enough to be His friend. There's no need for gnosticism (hidden knowledge) there's no need for new prophets like Muhammad, Joseph Smith or Mary Eddy. Likewise, there's no need for Marian apparitions at Fatima and Lourdes or the millions of miracles experienced by Christians over the centuries. But if these are the way Christ chooses to manifest Himself to His people, then that is His free choice. The Church just says, in the accordance with the Holy Spirit, there's no need for a Bible 2, even though the first one ends with "To be continued"...

For as the centuries succeed one another, the Church constantly moves forward toward the fullness of divine truth until the words of God reach their complete fulfillment in her.

Dei Verbum - 8

And, merely by building on the mysteries already given to us we'll continue to plumb the unfathomable depths of God until the end of time (which is hopefully soon).