The Meaning Of The Look Poem by Elizabeth Barrett Browning

I think that look of Christ might seem to say--
'Thou Peter ! art thou then a common stone
Which I at last must break my heart upon
For all God's charge to his high angels may
Guard my foot better ? Did I yesterday
Wash thy feet, my beloved, that they should run
Quick to deny me 'neath the morning sun ?
And do thy kisses, like the rest, betray ?
The cock crows coldly.--GO, and manifest
A late contrition, but no bootless fear !
For when thy final need is dreariest,
Thou shalt not be denied, as I am here;
My voice to God and angels shall attest,
Because I KNOW this man, let him be clear.'