# For we have the prophetic word made more certain

"For the things that we saw make this prophetic message more sure" or "the scriptures, which the prophets spoke, made". This refers to the Old Testament.  

# to which you would do well to pay attention

Peter instructs the believers to pay close attention to the prophetic message.

# as to a lamp shining in a dark place until the day dawns

Peter compares the prophetic word to a lamp that gives light in the dark until light comes in the morning. The coming of morning is a reference to Christ's coming.

# the morning star rises in your hearts

"Christ shines his light into your hearts like the morning star shines its light into the world"