Here Nephi quotes Isaiah, who speaks as if from Christ’s perspective. 

I have graven thee upon the palms of my hands – This imagery makes me think of Christ’s crucifixion and the suffering He went through for us.  It is as if we were the nails that pierced Him, and every time He looks at the marks in of the hands of His resurrected body, He remembers the sacrifice He made for us.

thy walls are continually before me – In one way, this can be interpreted to mean that Jesus is always watching over us, caring for us, and thinking of us.  In another way, it expresses how He knows the walls we have put up in our lives to try to keep Him out, and He wishes He could get through to us if we would only let Him.