Sorcha, A reasonable question. I think the answer is that, for those for whom the lyrics are an expression of faith rather than a cultural curiosity, what "sounds rather gruesome" is indeed a celebration of Love and Life. That the Son of God would offer His blood to save us from the guilt and consequences of sin is the ultimate expression of love. Christ's blood as that which cleanses is a theme that runs throughout the New Testament. Two passages alluded to in the hymn are Revelation 7:14 "…they have washed their robes and made them white in the blood of the Lamb," and I John 1:7 "the blood of Jesus Christ his Son cleanseth us from all sin."