These are some great words from Samuel Rutherford to his friend John Henderson. Rutherford wrote this from a prison in Scotland in 1637.
“Know the Lord and seek Christ. You have a soul that cannot die. Seek for a lodging to your poor soul, for that house of clay will fill. Heaven or nothing! Either Christ or nothing! Use prayer in your house and set your thoughts often upon death and judgment. It is dangerous to be loose in the matter of your salvation. ….Love your enemies and stand by the truth which I have taught you, in all things. Fear not men, but let God be your fear. Your time will not be long; make the seeking of Christ your daily task. Seek a broken heart for sin, for without that there is no meeting with Christ.”
You can find this quote on page 104 of the Puritan Paperback entitled The Letters of Samuel Rutherford. I especially like that sentence, which is a great commentary on Psalm 51.17.