What do Christians mean when they plead the blood of Jesus in prayer? Is there a canonical definition of the phrase? What do they expect will happen when they say it?
What is the biblical basis? Are there scriptural examples in which an apostle or a disciple pleaded the blood of Jesus for protection or any other purpose?
KB: I have heard Christians plead the blood of Jesus or the blood of the Lamb in prayer. In common usage, it's fairly simple. People seem to use this phrase to mean they are praying sincerely and in the name of Jesus. I am not disparaging anyone who prays with this phrase, just pointing out what I believe is the thought behind use of this phrase.
As used in the Bible this phrase certainly does have to do with spiritual warfare as we can see in this passage below.
Revelation 12:10-11 NIV:
Then I heard a loud voice in heaven say: “Now have come the salvation
and the power
and the kingdom of our God,
and the authority of his Messiah. For the accuser of our brothers and sisters,
who accuses them before our God day and night,
has been hurled down. 11 They triumphed over him
by the blood of the Lamb
and by the word of their testimony; they did not love their lives so much
as to shrink from death.
Another use is in Revelation 7:14 NIV
And he said, “These are they who have come out of the great
tribulation; they have washed their robes and made them white in the
blood of the Lamb.
I do not know of any Biblical example of someone praying by the blood of the Lamb. The phrase is used in various ways in the Bible as shown above, but it is not used Biblically in prayer as far as I know.