You and I have something wonderful about us that is unparalleled in all of God's creation. We are made in God's image. This means that we are personal, spiritual, and moral beings who can relate to God and be his representative rulers on earth. The ramifications of this are astounding, not the least of which is the sixth commandment, "You shall not murder." Human life is sacred because it reflects and represents God himself. That is certainly cause for joy.
But an even greater cause for joy is that God the Son was willing to humble himself to become one of us and thus to redeem us and make it possible for us to have that relationship with God that we were created to have. "Since therefore the children share in flesh and blood, he himself likewise partook of the same things, that through death he might destroy the one who has the power of death, that is, the devil, and deliver all those who through fear of death were subject to lifelong slavery" (Heb 2:14-15, ESV). Jesus Christ, the God-man, fulfills in himself all that mankind was designed to be, and he brings us with him as we are united to him. That is joyful indeed.
All Creatures of Our God and King (#59)
All Things Bright and Beautiful (#723)
It is Finished (#138)
Hallelujah! What a Savior (#128)
Salvation! O My Soul Rejoice (#291)
Once in Royal David's City (#91)
The Command to Love Human Life (Part 2) - Deuteronomy 5:17