This is one of Robert Murray McCheyne well known hymns. In McCheyne's writings it is entitled "The Watchword of the Reformers". The word "watchword" appears in the last verse and was placed in quotation marks in McCheyne's writings.
There are two more verse in the original poem that McCheyne penned than appears in the Free Presbyterian hymnal, see verse two and verse six. In his writings this poem was dated November 18 1834.
1. I once was a stranger to grace and to God,
I knew not my danger, and felt not my load;
Though friends spoke in rapture of Christ on the tree,
Jehovah Tsidkenu was nothing to me.
2. I oft read with pleasure, to sooth or engage,
Isaiah’s wild measure and John’s simple page;
But e’en when they pictured the blood-sprinkled tree
Jehovah Tsidkenu seem'd nothing to me.