# Hold on to the word of life

"Continue to firmly believe the word of life"  

# the word of life

"the message that brings life" or "the message that shows how to live the way God wants you to"

# on the day of Christ

"when Christ returns"

# I did not run in vain or labor in vain

"I did not work so hard for nothing" 

# run

The scriptures often use the image of walking to represent conducting one's life. Running is living life intensely.