It was the Hebrew custom to quote a phrase from a passage of Scripture with the understanding that the context of the quote was to be applied to the subject of discussion. It’s much like a bookmark.
In our English language we do the same thing. One example that comes to mind is “Don’t pay attention to him, he’s just crying Wolf”. That’s a common reference to the children’s teaching story about a shepherd boy who lied to get attention. After being fooled too many times, the town’s people quit believing his cries for help and didn’t come to his aid. So the boy ended up being eaten by the wolf.
When a person is said to be “crying wolf” it means he is lying and will end up being hurt because of his lies. The speaker of that common phrase assumes that the hearer is familiar with, and will apply, the whole story.
A example from the Bible is found in Hebrews 2:12 where it says: “So Jesus is not ashamed to call them brethren. He says, ‘I WILL PROCLAIM YOUR NAME TO MY BRETHREN, IN THE MIDST OF THE CONGREGATION I WILL SING YOUR PRAISE.’” That comes from Psalm 22:22. The implication is that there is much insight to be gained by reading more than just that one verse in Hebrews 2. Rather, take a look at the whole psalm and you will read Jesus’ entire experience on the cross. You see, the “congregation” identified here is the people to came to watch Him die!
So when a phrase from an Old Testament passage is quoted, the whole passage should be examined to understand the rest of the story. This is especially true with quotes referring to Jesus.