To JWs, how is Jesus Christ "the same yesterday and today, and forever"? I'm referring, of course, to Hebrews 13:8. The Jehovah's Witnesses' preferred translation, the New World Translation, translates it in basically the same way as all other translations:


  Jesus Christ is the same yesterday and today, and forever.


Many trinitarians see this verse as a reference to immutability, which is unquestionably an attribute of God and not of creatures. What do JWs see this verse as referring to? How can Jesus be "the same yesterday and today, and forever" if he is a creature?
Pretty simply, actually.  His pre-existence (yesterday) is explained as a special case:


  Unlike any other human, Jesus lived in heaven as a spirit person before he was born on earth. (John 8:23) He was God’s first creation, and he helped in the creation of all other things. He is the only one created directly by Jehovah and is therefore appropriately called God’s “only-begotten” Son. 


Jesus' resurrection returned him to his spirit-being (today and forever):


  After Jesus died, God restored him to life as a spirit person. (1 Peter 3:18) Jesus then waited at God’s right hand until Jehovah gave him power to rule as King over all the earth. (Hebrews 10:12, 13) Now Jesus is ruling as King in heaven, and his followers are announcing that good news worldwide


The quotes above are taken from the JW website and a publication titled "Who is Jesus Christ?"