Abdullah,
That is exactly what we are saying... that at the point of his death, the human Jesus took on the sin of the world, and BECAME sin for us. He didn't just take it on himself, he BECAME sin!
You are exactly right too.. God owes us nothing.. and we owe Him EVERYTHING.. so if the Bible is right, and if Jesus was sinless, and if God did arrange for Him to be the perfect sacrifice so that our sins could be taken on Him, so that He literally BECAME sin for us, and if we owe Him everything... Isn't it something we have to think seriously about if we say we believe in God and want to truly submit to Him?
If He loved us enough to actually come as man, take sin and become sin for us, to ensure we KNEW that nothing we do will earn us salvation.. or eternity with Him.. what right have we got to tell God we don't accept it? Which is worse? to tell God we think that what He alone did on the cross, is not true or to go through life hoping that God will accept us because of the good things we do?
You see, as Muslim, your observance of the arkan-ud-din, is based on you then doing it well enough to tip the scales in your favour on judgement day. That God will accept you.. Surah 35:7 says
For those who reject Allah, is a terrible penalty: but for those who believe And work righteous deeds, is forgiveness and a magnificent reward".
and Surah 23:102.103 says
"Of those whose balance (Of good deeds is heavy), they will attain salvation, but those whose balance is light, will be those who have lost their souls, in hell will they abide."
You do your best .. do lots of good works, and HOPE that Allah will bless you with your reward. Salvation for the Muslim, doesn't rely on Allah alone, but on your ability to show by your good deeds that you can balance the scales and be acceptable to him.
Christianity says.. that works will never save you.. it's a gift from God and the responsibility is on you to accept His way of salvation. (Ephesians 2:8-9)
For it is by (God's) grace you have been saved, through faith, and this not of yourself (even our faith is not from ourselves..but given by God), NOT BY WORKS so that no one can boast."
So who is showing more respect to God? The Muslim who does lots of good works and hopes to earn Allah's acceptance, or the the Christian who admits that there is nothing in him that could ever hope to meet the standard God sets, looks to God and sees that His Creator has done it all for Him? Who is showing the greater submission?
Hebrews 2:3-4 says
"how shall we escape if we neglect so great a salvation? This salvation was first announced by the Lord, was confirmed to us by those who heard him. God also testified to it by signs, wonders and various miracles..."