Isaac Watts' Hymn "At the Cross"

There's the Christian hymn that would describe Good Friday. Here are the lyrics of the song that would describe the true purpose of Jesus' death:
Alas! and did my Savior bleed
And did my Sov’reign die?
Would He devote that sacred head
For such a worm as I? 
Was it for crimes that I had done
He groaned upon the tree?
Amazing pity! grace unknown!
And love beyond degree! 
Well might the sun in darkness hide
And shut his glories in,
When Christ, the mighty Maker died,
For man the creature’s sin. 
Thus might I hide my blushing face
While His dear cross appears,
Dissolve my heart in thankfulness,
And melt my eyes to tears. 
But drops of grief can ne’er repay
The debt of love I owe:
Here, Lord, I give myself away,
’Tis all that I can do. 
Refrain (Hudson): 
At the cross, at the cross where I first saw the light,
And the burden of my heart rolled away,
It was there by faith I received my sight,
And now I am happy all the day! 
Refrain (Campmeeting): 
I do believe, I do believe
That Jesus died for me;
And through His blood, His precious blood
I am from sin set free.

The very song talks about how hard it is to believe that Jesus who knew no sin would die for the sins of mankind. The Gospel attacks the very core of the belief that humanity is basically good and salvation by one's own merit. The truth is there is no merit outside Jesus. No true righteousness outside Jesus. What Jesus did is hard to believe and hard to comprehend. It sounds absurd that the Son of God would voluntarily let all the blows of the world hit Him, that He should die a criminal's death when He had done nothing. Yet, the cross is the success of God that would provide salvation to all who would receive.

The song also talks about the true gratitude of true conversion. Drops of grief can't repay. The result of a true conversion is a life that wants to live for Christ. Anybody who thinks that they have a license for sin is a false convert. True converts don't want to live in sin anymore!

See also: