Heb 1:3 "Who being the brightness of [his] glory, and the express image of his "person" (hupostasis), and upholding all things by the word of his power, when he had by himself purged our sins, sat down on the right hand of the Majesty on high;"

The Greek word "hupostasis" means "to stand under", or "to take on one's self something else without losing what you had". The word "person" (Greek hupostasis) in Heb 1:3 speaks of the Second Person of the Trinity, Jesus Christ, as a whole "person", which consists of His divine and human nature.

---  In John 8:58, Jesus said "Verily, verily I say unto you, before Abraham was (existed), I am" . "I am" in this verse is the Greek phrase "ego eimi", meaning "the self existent one". The Hebrew rendition of this phrase came from the burning bush, when God spoke to Moses in Ex 3:14, and said to tell Israel that the "I AM" has sent me unto you. Jesus is calling himself God in this verse, the one who spoke to Moses from the burning bush! In Jn 8:59, His hearers took up stones to stone Him.

---  In John 3:12 & 13, Jesus told Nicodemus that He was in heaven as well as on earth as He spoke:

Jn 3:12 "If I have told you earthly things, and ye believe not, how shall ye believe, if I tell you [of] heavenly things?  And no man hath ascended up to heaven, but he that came down from heaven, [even] the Son of man which is (presently) in heaven."