The true meaning of Christmas is the celebration of the birth of Jesus who lived in Israel 2000 years ago and who died on the cross for our sins (1 Corinthians 15 1-4; 1 Peter 2:24). More specifically, when we use the word "meaning," we're talking about the purpose of his birth that Christmas is supposed to celebrate. His purpose was to enter into the world and become one of us, that he might deliver us from our sins. Jesus is not just any man. He is God in flesh (John 1:1, 14; Colossians 2:9). He is the second person of the Trinity who, by being born of the Virgin Mary, was made under the law (Galatians 4:4) and subject to the same temptations and limitations that we are. Christmas is the celebration of the historical event of where God entered into our world so that he might display the perfection and holiness of God and that through his work of living perfectly and also dying on the cross for our sins, that all who trust in him would be saved from the righteous judgment of God.
"For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life. 17 For God did not send the Son into the world to judge the world, but that the world might be saved through Him," (John 3:16-17).