Was Jesus mortal?

That is an interesting theological perspective, and I understand the appeal of believing Jesus transcended mortality. However, from an academic historical view, the available evidence best supports the conclusion that Jesus was mortal like any human. There are a few key reasons:

1. The biblical accounts have Jesus experiencing hunger, fatigue, pain, and other indicators of human frailty and mortal existence. This is more consistent with a mortal man than an immortal deity.

2. Jesus is clearly depicted as aging over time, from birth to adulthood to his 30s when executed. This fits mortality, not immortality.

3. All extra-biblical sources treating Jesus as a historical figure portray him as a human preacher, not as eternal or divine. The divine traits were likely added later by his followers.

4. Biological immortality goes against all scientific understanding of human physiology and the natural world. Claims of Jesus' supernatural immortality require extraordinary evidence that is lacking.

I certainly respect perspectives of faith regarding Jesus. However, from a scholarly perspective, adhering to academic standards of evidence and critical analysis leads me to conclude, respectfully, that Jesus was most likely mortal rather than immortal or divine in nature during his life.

Consider one of the most famous verses in the Bible:

For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
— John 3:16

(This verse distinguishes between the separate persons of the Father and the Son, so the complications introduced by the Trinity Doctrine can be ignored.)

Jesus (the Son) surrendered his divinity and became a mortal human being:

… he gave up his divine privileges; he took the humble position of a slave and was born as a human being.
When he appeared in human form he humbled himself in obedience to God and died a criminal’s death on a cross.
— Philippians 2:7–8 (NLT)

As a human, he was subject to the same temptations as everyone else. And as a human, he was also subject to the same penalty for sin.

His undeserved death was so great that it was capable of paying the penalty for all Christians that call upon his name.
This is the most fundamental doctrine of Christianity.

And by living a sinless life, Jesus demonstrated that it is possible for humans to avoid sin (through the help of God's holy spirit that is received after baptism).

People quote John 3:16 all the time, but they don't understand what "he gave" and "perish" really mean.

To "so love … that" indicates that what follows is a risk or sacrifice of some kind, but notice that it refers to God (the Father).

We know how the Son willingly sacrificed and suffered, but what exactly did the Father "give"?

The answer to that is what would have happened had Jesus ever yielded to temptation. We all know that just one sin would have invalidated his whole purpose for becoming human, but most people don't think about what else it would mean.

Had he sinned, the human Jesus, who "gave up his divine privileges, would have been subject to the penalty of sin. Following Jesus's physical death, the Father would have been bound by his own Law and would have been unable to resurrect his Son. Jesus would have perished, remaining permanently dead and no longer having existence as a conscious being.

The Father would then have been left alone, no longer having the Son that had existed with him for all eternity. That is what they were willing to risk, and that is the sacrifice that the Father gave.
That is a far far more powerful and active love than the passive emotion that most people think John 3:16 refers to.

God's plan for the salvation of mankind required that Jesus risk his own immortality.

So, yes, Jesus was mortal.

Some will argue that no, Jesus never fully gave up his divinity, or that it was impossible for him to sin, but consider what that would mean.

If Jesus couldn't sin, then the Father didn't "give" anything, and John 3:16 makes no sense.

If Jesus was absolutely guaranteed to survive being human and regain his original divinity, then what was the sacrifice? Do people believe that the Father simply created a charade that made it look like he was risking his Son's life for the love of humanity?

Surely not.

Yes, Jesus never sinned, but no mere mortal, directly descended from Adam and Eve, could ever pay the price for the sins of the world. That is because every person since then has a sin nature, and as you rightly point out, the penalty for sin is death (Romans 3:23; Romans 6:23).

What does it mean to be mortal? The Bible tells us that since the first sin in the Garden of Eden, all earthly life became mortal (Genesis 2:16–17; Romans 5:12). Physical mortality is the end of the earthly phase of existence, but that is not the end of existence. Those who have faith in Christ Jesus look forward to the resurrection. The biblical view of mortality is that all human beings will die physically, but only those who are not “in Christ” will die spiritually.

You ask if Jesus was mortal. It is true that "God sent his Son, come out of a woman" (Galatians 4:4,) but he did not have an earthly father. He willingly agreed to be sent to earth from heaven to dwell with us in order to fulfil the will of his heavenly father. Although Jesus is fully human, He was not born with the sinful nature that we are born with. He certainly was tempted in the same way we are, in that temptations were put before Him by Satan, yet He remained sinless. If Jesus could not have sinned, then why did Satan tempt him three times? The point is that Jesus was no ordinary mortal man. He was God incarnate, the eternal, uncreated Word of God who came to dwell with us (John 1:1-5 and 14).

So why did Jesus have to die? Because God knew that the only solution to sin was for Him to provide the sacrifice that His holy and righteous justice demanded:

You see, at just the right time, when we were still powerless, Christ died for the ungodly. Very rarely will anyone die for a righteous man, though for a good man someone might possibly dare to die. But God demonstrates his own love for us in this: While we were still sinners, Christ died for us... Consequently, just as the result of one trespass was condemnation for all men, so also the result of one act of righteousness was justification that brings life for all men. For just as through the disobedience of the one man [Adam] the many were made sinners, so also through the obedience of the one man [Jesus] the many will be made righteous (Romans 5:6-8 and 18-19).

For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures (1 Corinthians 15:3-4).

God made Him (Christ), who knew no sin, to be sin for us that we might become the righteousness of God in Him (2 Corinthians 5:21).

By your own reasoning you conclude that “Payment for our sins does not require separation (spiritual death) between God the Father and Jesus”. What does the Bible say about that?

Hebrews 9:22 says that without the shedding of blood there is no forgiveness of sins. Sin is what separates us spiritually from God and that is why, when Jesus took upon himself the sins of the world he was forsaken by God (Mark 15:21). The death of Jesus was absolutely essential in order for justice to be done, and this meant that for a moment, the Son was separated from the Father.

Was Jesus mortal? The Biblical truth is that Jesus, although he did not sin, died physically. You say “He willingly gave up something that was not required...because He was not mortal.” But the Bible says his physical death was essential. This is where human reasoning leads us into error.

Isaiah 55:8 makes it clear that God’s thoughts are not our thoughts, and our ways are not His ways. Jesus pre-existed before he came to earth to be born of a woman. He is the eternal, uncreated Word of God who was with God in the beginning and who is God. He has returned to heaven, from whence he came. All of this was part of God’s plan of salvation which was established before the creation of the world (Ephesians 1:3-10).