Jane,
Gibran once noted that we can give people our words but not our understanding. That is why I suggest you reference people like C.S. Lewis who are better teachers than I. But I guess to be fair (to me) I need to tell you what I do believe rather than being judged on what I reject.
I believe that Christ suffered and died by the will and predetermined plan of God by the hands of wicked men for our sins in order to redeem (or purchase) us and deliver us from the bondage of the powers of sin and death that had enslaved us. I believe that God offered His Son (His Righteous One) as a sin offering for us and that it pleased God to "crush" Him, that He (Christ), who knew no sin was made sin for us. I believe that Christ humbled Himself to obedience even to death on the cross and that He lay down His own life. I believe that Christ is the Propitiation for the sins of the whole world and that it is in Him we escape the wrath to come. He became a curse for us and it is by His stripes (His suffering and death) that we are healed. Christ destroyed the certificate expressed in decrees against us. He has taken it away by nailing it to the cross. Christ suffered once for sins - the Just for the unjust (this "great exchange") to bring us to God by being put to death in the flesh and by being made alive in the spirit.
@David Taylor ,
@Steve Owen , and
@Enoch111 view my belief above as heresy because it does not include their theory. I believe their belief (Penal Substitution Theory as stated in the OP) is heresy because it does include their theory. We cannot give people our understanding but at least we can know where we stand in terms of beliefs.
I hope that explains what I believe, even if you find it less than sufficient a belief for you to hold. My intent is not to convert people to my understanding but to hopefully let people know what I believe and perhaps encourage them to constantly reexamine their own beliefs against Scripture.
John