Mosiah 3

As King Benjamin spoke concerning the mortal life of the Savior, he prophecied that -

"...he shall suffer temptations, and pain of body, hunger, thirst, and fatigue, even more than man can suffer, except it be unto death..." (Book of Mormon | Mosiah 3:7)

Thus as explained later by Alma -

"...he shall go forth, suffering pains and afflictions and temptations of every kind; and this that the word might be fulfilled which saith he will take upon him the pains and the sicknesses of his people.
12 And he will take upon him death, that he may loose the bands of death which bind his people; and he will take upon him their infirmities, that his bowels may be filled with mercy, according to the flesh, that he may know according to the flesh how to succor his people according to their infirmities." (Book of Mormon | Alma 7:11 - 12)

Thus having a full understanding how to succor his people, He -

"...shall go forth amongst men, working mighty miracles, such as healing the sick, raising the dead, causing the lame to walk, the blind to receive their sight, and the deaf to hear, and curing all manner of diseases." (Book of Mormon | Mosiah 3:5)

And as he did -

"...he shall cast out devils, or the evil spirits which dwell in the hearts of the children of men." (Book of Mormon | Mosiah 3:6)

Knowing that evil spirits are personages of spirit, it is obvious that they could not literally dwell in the hearts of men. I beleive then that the wording "dwell in the hearts of the children of men" would suggest evil thoughts, anger, hatred, contention, wicked desires and so forth. Thus the Savior not only had the ability to cast out spirits but also change and heal ones heart or desires. Alma would later share of his father's followers speaking of the Savior, that -

"...he changed their hearts..." (Book of Mormon | Alma 5:7)

Thus King Benjamin would later acknowledge to his people -

"...he hath spiritually begotten you; for ye say that your hearts are changed through faith on his name..." (Book of Mormon | Mosiah 5:7)

I believe this is synomous to the Savior casting out evil spirits in the heart of men. I believe this is more of a process than a single event Thus, as evil is cast out by faith in his name, though we may not be perfect, King Benjamin taught -

"...the Lord hath heard thy prayers, and hath judged of thy righteousness, and hath sent me to declare unto thee that thou mayest rejoice; and that thou mayest declare unto thy people, that they may also be filled with joy." (Book of Mormon | Mosiah 3:4)

Though we may not yet be perfect, we may still rejoice in the process.