What does the Lord Jesus mean when He said "And I will raise him up at the last day' Jn.6:44?

Yes. He raises people from the dead everyday all over the world. Jesus is talking about the dead in Christ. Meaning they were born again and died physically. Their bodies are in the ground. Their soul and spirit are in Heaven. His Word tells us to be absent from the body is to be present with the Lord. At the rapture dead in Christ will be raised with incorruptible bodies. They will be reunited once again body, spirit and soul. Their new bodies will be without spot or blemish. It will be their glorified bodies and they will look as Jesus looks right now. The second coming is not the same thing so don't get them confused. When the rapture takes place Jesus will not touch the Earth and no one will see Him but, those that meet Him in the clouds. At the second coming He will come back the same way He left on the Mt. of Olives and He will destroy the wicked and put an end to the final war in Armageddon. At His second coming every eye will see Him and everyone will confess He is King of Kings and Lord of Lords and every knee will bow to Him. All things in Heaven and on Earth and beneath the Earth. I hoped this helps. He is coming anytime now so please be ready. No one knows the date or hour but, The Father. So don't believe the false doctrines out there that give a date. God is very upset with them for misleading people. That is an understatement actually. Feel free to email me with more questions if you like. God bless you and keep you in His loving arms.