(Ephesians 2:1-5 KJV)  And you hath he quickened, who were dead in trespasses and sins: {2} Wherein in time past ye walked according to the course of this world, according to the prince of the power of the air, the spirit that now worketh in the children of disobedience: {3} Among whom also we all had our conversation in times past in the lusts of our flesh, fulfilling the desires of the flesh and of the mind; and were by nature the children of wrath, even as others. {4} But God, who is rich in mercy, for his great love wherewith he loved us, {5} Even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;)

We, who were dead, are now quickened. There is an issue of death, when Adam was created there was no issue of death. Adam was created to live forever.

There are five different kinds of death mentioned in the scripture. Just as we need to find the proper definition of the use of a word when looking a word up in the dictionary so must we correctly define the term "death" .

Five kinds of death

1. Physical Death

   (2 Corinthians 5:8 KJV) We are confident, I say, and willing rather to be absent from the body, and to be present with the Lord.

   Physical death is to be separated from body. When the soul is absent from the body, it is physical death. To be absent from the body means there is a physical separation from the body.
   
   

2. Separation From God For Eternity

   (Revelation 20:13-15 KJV)  And the sea gave up the dead which were in it; and death and hell delivered up the dead which were in them: and they were judged every man according to their works.{14} And death and hell were cast into the lake of fire. This is the second death. {15} And whosoever was not found written in the book of life was cast into the lake of fire.

   At the great white throne judgment, those who were not written in the book of life are cast into the lake of fire. This is the second death, which is separation from God for eternity.

   (Revelation 21:8 KJV)  But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death.

   The second death is the lake of fire, or the second separation from God.

3. Positional Death

   (Romans 6:3-4 KJV)  Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death? {4} Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.

   We have died with Christ at Calvary. We, as believers in what Christ has done for us, have been baptized into Christ's death. This means that we have died with Christ when He died on Calvary.

   (1 Corinthians 12:13 KJV)  For by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit.

   It is by the Spirit that we are baptized into the Lord Jesus Christ; we are buried with him through baptism. We are dead in Christ therefore we should now walk in newness of life.

   (Romans 6:6 KJV)  Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin.

   Our old man, who we were in Adam, is crucified with Christ. Positionally, we are crucified with Christ. God no longer sees us in our sinful state; He sees us as who we are in Christ, as Christ died so did we.

   Have you ever seen a dead man sin?  If you are dead then you are free from sin.  We need to understand who we are in Christ.  (Romans 6:14)

   (Galatians 2:20 KJV)  I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.

   I am crucified with Christ. When Christ died on the cross, He was made to be sin. Christ died that second death for us.  The issue is not just dying with Christ, Christ also rose from the dead. Just as we died with Christ, we also live with Christ.

   (2 Corinthians 5:14-15 KJV)  For the love of Christ constraineth us; because we thus judge, that if one died for all, then were all dead: {15} And that he died for all, that they which live should not henceforth live unto themselves, but unto him which died for them, and rose again.

   We should no longer want to live our own life but we should live by the faith of Christ, that is allowing Him be faithful to what He said He would do in our lives.
   
   

4. Functional Death

   (Romans 4:19 KJV)  And being not weak in faith, he considered not his own body now dead, when he was about an hundred years old, neither yet the deadness of Sarah's womb:

   Abraham considered his own body now dead.  Abraham was alive when he considered this.  The scriptures also speak of the deadness of Sarah's womb.  In this context, dead means not functioning, not producing. 

   If we are not living the way we should be living, we are functionally dead, not producing what we are to be producing.  We are acting as a lost man that is, one who is functionally dead, unable to be used of God. Often we assume if one is not living a certain way then they are not saved. This is not true. They are simply not living the life they ought to and are not producing anything useful to God. They are not functioning in the manner in which God would have them to function. This does not mean they are not saved.

   (Romans 8:5-8 KJV)  For they that are after the flesh do mind the things of the flesh; but they that are after the Spirit the things of the Spirit. {6} For to be carnally minded is death; but to be spiritually minded is life and peace. {7} Because the carnal mind is enmity against God: for it is not subject to the law of God, neither indeed can be. {8} So then they that are in the flesh cannot please God.

   To be carnally minded is to be functionally dead not lost.  If one is living after the flesh, it does not mean they are lost but rather functionally dead.

   (Romans 8:1 KJV)  There is therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit.

   If we walk after the flesh, the law will condemn us.

   (Galatians 5:16-18 KJV)  This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh. {17} For the flesh lusteth against the Spirit, and the Spirit against the flesh: and these are contrary the one to the other: so that ye cannot do the things that ye would. {18} But if ye be led of the Spirit, ye are not under the law.

   Someone who is led of the Spirit is not under the law. Someone living under the law is living in the flesh.

   (1 Corinthians 3:1 KJV)  And I, brethren, could not speak unto you as unto spiritual, but as unto carnal, even as unto babes in Christ.

   Why did Paul have to talk to the Corinthians as carnal? He did so because they were minding the things of the flesh.  Paul also called them saints, sanctified, he was not saying they were lost because they were carnal. The things they were doing were carnal, they were not showing who they were in Christ.  They were functionally dead, not living according to who they were in Christ.
   
   

5. Spiritual Death

   (Ephesians 4:17-18 KJV)  This I say therefore, and testify in the Lord, that ye henceforth walk not as other Gentiles walk, in the vanity of their mind, {18} Having the understanding darkened, being alienated from the life of God through the ignorance that is in them, because of the blindness of their heart:

   When we were dead in our trespasses and sin, we were alienated from the life of God. The spirit is dead, not having the life of God.

   (2 Corinthians 5:14 KJV)  For the love of Christ constraineth us; because we thus judge, that if one died for all, then were all dead: 

   If one died for all, then all were dead; all were spiritually dead.

   (Ephesians 2:1 KJV)  And you hath he quickened, who were dead in trespasses and sins:

   You were dead in trespasses and sin, we all broke the law (God's standard of righteousness). All have sinned and come short of the glory of God.  We could not reach the glory of God.  However, God has made us alive, he has quickened us.  He made us alive in Christ.  Christ paid dead sin dead for us.  He died for second death so that we would not have to die.  We could not do it anything but failed to attain the righteousness that God required.  While trying to do it ourselves, we just got ourselves deeper and deeper in debt.  Christ did it all for us and all we have to do is trust and rely on what Christ did. 

   (Ephesians 1:13 KJV) In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,

   We have hope because we believe Jesus died and rose again.  We heard the gospel of grace and believed it.

   (1 Corinthians 15:3-4 KJV)  For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; {4} And that he was buried, and that he rose again the third day according to the scriptures:

   Our spirit is no longer dead and we now have a part in the life of Christ.  By God's grace, He saved us through faith by the blood of Christ. He has quickened us and made us alive.
   

Reference:
My notes from teaching by Keith Baxter and KJV Bible