Jesus did NOT commit suicide. Does a soldier who throws himself on a hand grenade commit suicide or is he martyring himself for the sake of saving others? Christ did not kill Himself. When a soldier goes on a mission, he is not going to be killed, he's going on a mission to be completed. If he is killed during that mission, regardless of how, we do not say that he was went to kill himself. We never say our soldiers are suicide soldiers out to commit suicide. That is ridiculous! But we DO know that there IS a chance, and sometimes a GOOD chance, that the soldier is not going to return alive because they, too, are in harm's way.
As for it being a death on the cross, specifically, NO... it really did NOT matter HOW he was killed. But God's omniscience allowed Him to know beforehand that the manner of Christ's death would be upon a cross. If it had been in a lions' den or fiery furnace, then Scripture would have told us this instead. But one thing is for sure, it DID HAVE to be a BLOOD sacrifice.... it HAD to be in a method which spilt blood... because God demanded a BLOOD sacrifice for the atonement of sins. So "any form of murder" would NOT bring the same results, ONLY one which would involve the spilling of innocent blood.
Well... to be truly TECHNICALLY correct, it is NEITHER His physical or spiritual death which saves us. Those are actually the PRICE of our sins.... Scriptures says that the PRICE of sin is DEATH... both physical death AND spiritual death (separation from God). Christ PAID that PRICE.
And so, the story COULD have ended RIGHT THERE, and salvation/restoration back to God would NEVER have actually been obtained.
And THIS is where Christ, being FULLY human and FULLY GOD was SO important.
You see... WE HUMANS can and DO pay the price for our sins... we DO DIE both physically AND spiritually. But that's ALL WE CAN DO! We do NOT have the power within OURSELVES to resurrect OURSELVES back to life physically or spiritually. But...
JESUS CAN!! Because Jesus is FULLY GOD, He had the power within HIMSELF to RESURRECT HIS OWN physical body AND bring His spirit out from hell (separation from God) and restore Himself to the Right Hand of God the Father. If we COULD accomplish this ourselves, then there would be NO NEED for Christ and His death/resurrection, would there? But...
WE CANNOT DO this for ourselves. But Christ DID accomplish this feat.... and He says to us, "I did this FOR you, in your stead, because you could not do this for yourselves, and because I love you so much, I now offer to you, by virtue of MY accomplishment that same accomplishment to YOU!"
THIS is the Gospel... THIS is the salvation... THIS is the restoration of our selves to God... THIS is what SAVES us from sin.
MARANATHA! Come, Lord Jesus, COME!