Jesus said if you look upon a woman to lust after her you have already commited adultery with her in your heart.
Does this mean temptation is a sin by itself?
Jas 1:12 Blessed is the man that endureth temptation: for when he is tried, he shall receive the crown of life, which the Lord hath promised to them that love him.
If a person is blessed for enduring temptation then temptation is not a sin.
Jas 1:13 Let no man say when he is tempted, I am tempted of God: for God cannot be tempted with evil, neither tempteth he any man:
Jas 1:14 But every man is tempted, when he is drawn away of his own lust, and enticed.
Jas 1:15 Then when lust hath conceived, it bringeth forth sin: and sin, when it is finished, bringeth forth death.
Jas 1:16 Do not err, my beloved brethren.
Temptation is not a sin unless someone acts upon it.
1Co 10:13 There hath no temptation taken you but such as is common to man: but God is faithful, who will not suffer you to be tempted above that ye are able; but will with the temptation also make a way to escape, that ye may be able to bear it.
Temptation is not a sin which all people will be tempted and God will give them an escape from the temptation so they can bear it.
It is like the saying you can lead a horse to water but you cannot make it drink.
A temptation is only a thought and is not a sin unless acted upon.
Heb 4:15 For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin.
Jesus was in all points tempted like as we are, yet without sin.
So temptation is not a sin and Jesus is sinless but He was tempted.
Mat 5:28 But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.
Lust is not a temptation but an act of willingly wanting to entertain the woman.
Temptation is not the act of sin.
Lust is the act of sin in your mind which is the same as if you did the act.
If you see a muscle car in show room condition you will think that is a nice looking car.
If you see a nice looking woman your mind will think that it is a nice looking woman.
What else is your mind going to think.
So it is not a sin unless acted upon.