The Greek word for immortality is athanasia, and it is indicative of one who cannot die. (Strong's Exhaustive Concordance of the Bible In his letter to Timothy, Paul wrote about God: "Who only hath immortality, dwelling in the light which no man can approach unto; whom no man hath seen, nor can see: to whom be honor and power everlasting. A-men." (I Timothy 6:16, KJV) The New Living Translation renders this verse: "He alone can never die, and he lives in light so brilliant that no human can approach him. No human eye has ever seen him, nor ever will. All honor and power to him forever! Amen." Hence, we can see that Paul clearly believed that immortality was a God quality - something uniquely belonging to God.
Where did Paul get such an idea? Is that notion consistent with what is revealed elsewhere in Scripture?
God revealed to Moses that "He" was the "I am." (Exodus 3:14) The Hebrew word is hayah, and it means to exist or be in existence. (Strong's) So God is literally saying to Moses that "I am the one who exists because I exist." In other words, "He" is the Self-existent One - the One who doesn't need any outside force to sustain himself. Thus we see that Paul's notion about immortality being a unique quality of God is consistent with what was revealed to Moses.
Apparently God and Jesus Christ sustain all other life forms that they created. (Hebrews 1:3)
What about humans? Paul told the saints at Corinth that immortality was something that they would one day acquire, but that they were not born with it. In explaining to them the concept of the resurrection, he wrote: "Now this I say, brethren, that flesh and blood cannot inherit the kingdom of God; neither doth corruption inherit incorruption. Behold, I shew you a mystery; We shall not all sleep, but we shall all be changed, In a moment, in the twinkling of an eye at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed. For this corruptible must put on incorruption, and this mortal must put on immortality. So when this corruptible shall have put on incorruption, and this mortal shall have put on immortality, then shall be brought to pass the saying that is written, Death is swallowed up in victory." (I Corinthians 15:50-54
What about angels? Although angels apparently have the ability to exist indefinitely (Satan, Michael and Gabriel are mentioned in Scripture over long expanses of time), it is still clear that they exist at God's pleasure - that they are not self-existent. In this connection, notice that it is mentioned in several different places in the Bible that Satan will someday cease to exist. (Isaiah 14:15, Ezekiel 28:16-19 and Revelation 20:10)
Doesn't the last scripture referenced (Revelation 20:10) indicate that Satan will be tormented forever? If that is what is indicated, then it contradicts the scripture which refers to the Lake of Fire as the "second death." (verse 14) Notice that this same scripture also indicates that death and the grave will be cast into the same Lake of Fire. Moreover, we read in the very next chapter about a new heaven and earth: "And God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away." (Revelation 21:4) One question comes to mind: How can the continued existence of anyone in a state of torment be consistent with this scripture?