At the instant of His conception, Jesus Christ became one person with two natures: one divine and one human. A nature can be thought of as a complex collection of attributes and not a substantive entity. A divine nature is a complex collection of attributes associated with God (i.e. transcendence; immanence; infinitude; eternality; immutability) while a human nature is a complex collection of attributes associated with humans (i.e. physical body; soul comprising heart, will and intellect). At conception, Jesus, who was already divine, became fully human. This was a great risk for God because humans are generally eager to embrace sin while only a sinless Jesus could accomplish the substitutionary atonement.
The spotless lamb, “without blemish,” was required for the Passover (Ex 12:5) and the words, “without blemish,” constantly recur in the descriptions of the sacrifices which pointed forward to the atonement accomplished by Christ. The Scriptures are completely unanimous in declaring the perfect sinlessness of Christ under all circumstances. The sinlessness of Christ is not merely a personal attribute, characteristic of His human nature as well as His divine nature, but it is an attribute which is absolutely essential to the atonement.
Regarding human sin, God is just. God does not impute to us the individual sins of Adam and Eve. But He knew it would be pointless to allow the offspring of Adam and Eve to be born sinless. He knew they would follow exactly the same path as their created ancestors. So He allowed the generations of Adam and Eve’s offspring to be born with a sin nature. We are all born corrupt, averse to God and inclined to evil. However, for this depraved nature we are not responsible and no guilt or demerit attaches to it. We become responsible for this sin nature only after attaining the age accountability and ratifying it as our own. The age of accountability is not the same for all persons and, for many, it may be very young indeed.
In contrast with the rest of the human race, Jesus was not conceived by a human father and was not born with a sin nature. Consequently, when He reached the age of accountability, He did not ratify a sin nature as His own. But He was fully human and was, therefore, fully capable of being tempted by sin (Heb 2:18, 4:15). Chapter 4 of Luke describes three powerful temptations He endured during His forty days in the wilderness. So even without a sin nature, Jesus could have succumbed to something called desire or evil impulse or lust.
Let no one say when he is tempted, ‘I am being tempted by God’; for God cannot be tempted by evil, and He Himself does not tempt anyone. But each one is carried away and enticed by his own lust. Then when lust has conceived, it gives birth to sin; and when sin is accomplished, it brings forth death (Jam 1:13-15).
Jesus experienced all normal human motivations such as hunger, thirst, weariness, sexual desire and loneliness. The one exception to human experience we find in Jesus is that He did not sin. He experienced desire, but He did not seek to satisfy those desires by sin.
For we do not have a high priest who cannot sympathize with our weaknesses, but one who has been tempted in all things as we are, yet without sin (Heb 4:15).
However, there is no reason to believe that Jesus was tempted by every single evil impulse throughout the history of the human race. For example, there is no reason to believe that Jesus ever desired to: engage in bestiality, murder his father, betray His mother’s trust or speak evil for personal gain. Yet these activities have been pursued, by others, countless times over the millennia. So when it seems like you are about to be carried away by a particular lust, don’t assume Jesus experienced that exact same lust and, even if He did, He did not give in to it! Just because Jesus understands your struggle, that gives you no license to embrace the sin. In the absence of confession, remorse, repentance, faith and obedience, Jesus will not give you a pass!