"Could Jesus have sinned? If He was not capable of sinning, how could He truly be able to 'sympathize with our weaknesses' (Hebrews 4:15)? If He could not sin, what was the point of the temptation?"
Answer: No, Jesus could not have sinned. If He could have sinned, He would still be able to sin today because He retains the same essence He did while living on earth. He is the God-Man - and will forever remain so, having full deity and full humanity so included in one person as to be indivisible. To believe the Jesus could sin is to believe that God could sin. Colossians 1:19, "For it pleased the Father that in Him all the fullness should dwell." Colossians 2:9, "For in Him dwells all the fullness of the Godhead bodily."
Although Jesus is fully human, He was not born with the same 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 remained sinless because God is incapable of sinning. It is against His very nature (Matthew 4:1; Hebrews 2:18, 4:15; James 1:13). Sin is by definition a trespass of the Law. God created the Law, and the Law is by nature what God would or would not do; therefore, sin is anything that God would not do by His very nature.
To be tempted is not in and of itself sinful. A person could tempt you with something you have no desire to do, such as to smoke crack or participate in a homosexual act. You probably have no desire whatsoever to take part in these actions, but you were still tempted because someone placed the possibility before you. There are at least two definitions for tempted:
1) Tempted - To have a sinful proposition suggested to you by someone or something outside yourself or by your own sin nature.
2) Tempted - To consider actually participating in a sinful act and the possible pleasures and consequences of such act to such a degree that the act is already taking place in your mind.
The first definition does not describe a sinful act/thought, the second does. When you dwell upon a sinful act and consider how you might be able to bring it to pass, you have crossed the line of sin. Jesus was tempted in the fashion of definition 1, except that He was never tempted by a sin nature because it did not exist within Him. Satan proposed certain sinful acts to Jesus, but He had no inner desire to participate in the sin. Hence, He was tempted like we are but remained sinless.
Jesus knows what it is like to be tempted, but He does not know what it is like to sin. This does not prevent Him from assisting us. We are tempted with sins that are common to man (1 Corinthians 10:13). These sins generally can be boiled down to three different types: the lust of the eyes, the lust of the flesh, and the pride of life (1 John 2:16). Examine the temptation and sin of Eve as well as the temptation of Jesus, and you will find that the temptations for each came from these three categories. Jesus was tempted in every way and in every area that we are, but remained perfectly holy. Although our corrupt natures will have the inner desire to participate in some sins, we have the ability to "just say no" to sin because we are no longer slaves to sin but rather slaves of God (Romans 6, especially verses 2 and 16-22).
http://www.gotquestions.org/could-Jesus-have-sinned.html
