The two testaments of the Bible are covenants or wills between God and mankind. The inheritance which heirs receive under either covenant is everlasting life. Each Bible testament describes the path to everlasting life for mankind under that particular covenant.
The path to eternal life under the first covenant was to never sin (Romans 6:23). However, there was a fault in the first testament in that all mankind sinned! (Romans 5:12) Since the first covenant contained a fault, God created a second or New Testament (Hebrews 3:6).
Under the New Testament Covenant, one must believe in Jesus as their Savior to gain everlasting life (John 3:16). Here is how that came to be:
The Word (a Spirit) was made flesh as the man Jesus Christ (John 1:14). Being a man (1Timothy 2:5), Jesus was included as a possible beneficiary under the original covenant between God and mankind.
In fact, Jesus became the only human to become an heir to immortality under the Old Testament Covenant! (1 Timothy 6:16).
His future inheritance belongs solely to Him, it is His possession, He owns it! And He is the only human that "hath immortality" as an inheritance.
But Jesus freely chooses to offer His inheritance as a gift to humans who believe in Him as their Savior. This is codified in the New Testament Covenant! (John 3:16)
But how can the one everlasting life which is Jesus' inheritance be distributed to more that one believer? Here's how that is justified in the scriptures:
Since many sinned due to one man (Adam), it is only fair that likewise many should be saved by the gift of everlasting life offered freely by the one man, Jesus Christ. (Romans 5:15)
Once the Word was made flesh as Jesus, Jesus had no choice but to die His first death – as it is appointed unto man once to die. So Jesus’ death, while required, is not what saves us.
What saves us is that Jesus offers His just inheritance of everlasting spiritual life received by His living a sinless life under the Old Testament Covenant to those humans who accept Him as their Savior from the wages of their sins under the New Testament Covenant.
Believers receive their inheritance of everlasting life by being born again of the Spirit (John 3:6) at the second Coming (Romans 5:15).
Conclusion: Whosoever believeth shall be born again of the Spirit, as a spirit, into the spiritual Kingdom of God, at the Second Coming. When this occurs, we will become equal unto the angels.
That is how any human may become an angel.

If you want to debate the above explanation, please do so with scripture references to support your claims.