Temptation is a word which is more commonly associated with inducement towards action of some kind - thinking, speaking or doing, whereas the trials mentioned in the previous verses concern forbearance, which is a passive attitude.
It is most important to understand and always bear in mind this radical difference:
Testing under trial: we are tested by God and should rejoice in this because it allows us to prove our faith and it strengthens us to endure greater things. God will allow Satan to do the testing, as in the case of Job, and of the Lord Jesus himself.
Solicitation to evil: God never induces us to sin: temptation to do evil is only possible to those who have an evil nature, such as the human nature of which we are being saved. God has a holy nature so it is impossible for Him to be tempted to do evil, or to induce any man to do evil, for this in itself would be evil and contrary to His nature. People tend to often blame God for a great many things for which only they themselves are responsible.
Just as trials are designed to bring out the best in us, temptations reveal the worst in us. The noun temptation, or trial, which was used before to convey a passive attitude is not used here, but the verb tempted meaning action.
It is typical of fallen human nature to find others to blame for all his own fumbles, all of his foibles, all of his faults and failures and filth. We see this at the very beginning, when Adam said, "The woman whom You gave to be with me, she gave me of the tree, and I ate." and Eve said "The serpent deceived me, and I ate." (Genesis 3:12,13).
Some try to blame animals and inanimate things for sin. But such creatures and objects aren't sinful in themselves therefore sin cannot originate there.
Others blame Satan and the forces of evil: they are, indeed, evil in themselves and they are capable of providing the opportunity, the desired bait. But the desire has to be there first in order for man to be tempted.
If an atheist cannot find someone else to blame, and is perceptive enough not to blame animals and objects, he will try to excuse himself by saying that sin is a sickness. Although sickness is used in Scripture as a type for sin, sin isn't sickness but it is a moral failure for which there is only one possible remedy: faith in the Son of God, Jesus Christ.
As a fish is only allured by bait which pleases it, man must have a personal desire for something in order to be tempted. Sin comes from within us, from our old, evil, fallen, unregenerate nature. As the Lord Jesus himself said: "… out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies." (Matthew 15:19).
The word in Greek used for desires in verse 14 is morally neutral and could refer to any form of desire, good or evil. Here, however, it is obviously meaning evil desires. We have vile lusts and impure appetites constantly urging us to sin, given the opportunity. All of us have our own particular evil desires. One person may be tempted to indulge in alcoholic drink. Another may be tempted to overeat. Another may be tempted in immorality. The problem is always within the individual. No outside thing or influence can make us sin. The trouble is here, within us, with that old nature that we have.
But we are not helpless victims of the bait which we are offered, or of an opportunity which arises. We are responsible for the action of accepting it or of taking advantage of it: it was done from our free will, because we desired it.
As born again believers, we are provided with new powerful defences:
By practising self-control, we can deaden the "old nature" within us "that you put off, concerning your former conduct, the old man which grows corrupt according to the deceitful lusts, and be renewed in the spirit of your mind, and that you put on the new man which was created according to God, in true righteousness and holiness." Ephesians 4:22-24.
By expelling all thoughts of sin from our minds and concentrating on subjects that are pure and holy (Philippians 4:8).
In the moment of fierce temptation we may call on the Lord, remembering that "The name of the LORD is a strong tower; the righteous run to it and are safe." (Proverbs 18:10)
Temptation by itself isn't sin. Sin only comes into existence when there is a will to give in to temptation. Martin Luther said: "You cannot keep birds from flying over your head, but you can keep them from nesting in your hair."
We can all be tempted to do evil: one may have an urge to be a glutton and another may cherish gossip. Both sins are absolutely of the flesh, but we shall only be guilty of them if we actually have a will to fall into them. As the Lord Jesus taught "whoever looks at a woman to lust for her has already committed adultery with her in his heart." (Matthew 5:28). The sin is there even though it is not yet "fully grown".
The word death here primarily means "separation." When we read "the wages of sin is death" (Romans 6:23), it is the separation of the sinner from God's presence, because He is holy. Adam and Eve lost their fellowship with God when they sinned, and were banned from His presence. Their physical death came centuries afterwards as a consequence of this banishment and has been inherited by all their descendants.
By the grace of God, however, it is possible for anyone to be received again by Him through faith, because He loved the world and had mercy on it, giving His only begotten Son as a price for redemption for our sins.
A believer will never again be banned from God's presence, and this is what is meant by "eternal life". It will never be taken away from him.
Yet his fellowship with God can be tarnished by sin. If sin is born in his life, and it becomes an action, his fellowship with God is broken and there is a separation, even though he is not banned from God's presence because Christ has suffered the punishment for it. Such lack of fellowship with God is, to a believer, a form of living death.
For example:
"… she who is really a widow, and left alone, … who lives in pleasure is dead while she lives." (1 Timothy 5:5-6). This is a sense in which the believer's sin results in death: the believer is wasting his life in pleasure and the luxuries of life without fulfilling the purpose for which God saved him.
We are told "If we say that we have fellowship with him, and walk in darkness, we lie, and do not the truth." (1 John 1:6). We cannot have fellowship with Him and permit sin continually to happen in our life.
Also: "But let a man examine himself, and so let him eat of the bread and drink of the cup. For he who eats and drinks in an unworthy manner eats and drinks judgement to himself, not discerning the Lord's body. For this reason many are weak and sick among you, and many sleep." (1 Corinthians 11:28-30). Sin will bring forth separation of fellowship with God and He will judge us for it unless we judge ourselves, confess our sin and mend our ways.
We are told not to be deceived, or not to wander, to roam about, or to stray. It is like the lost sheep the Lord Jesus told about which the shepherd went out after. We are not to deceive ourselves into thinking that somehow we can get by with sin. It is the way of sin to deceive and to kill (Romans 7:7-14). The devil is a past master at blinding men's eyes about sin (2 Corinthians 4:4; Romans 1:27; Ephesians 4:14; etc.).
13 Let no one say when he is tempted, "I am tempted by God"; for God cannot be tempted by evil, nor does He Himself tempt anyone.
14 But each one is tempted when he is drawn away by his own desires and enticed.
15 Then, when desire has conceived, it gives birth to sin; and sin, when it is full-grown, brings forth death.
16 Do not be deceived, my beloved brethren.