That ps is for you to express your most sincere intimate feelings for your reader that the card did not express. If you are like me, I take a few minutes to really think about what I want to say and how I want to convey it. Will you take a moment and think of what the Lord means to you? After you have done so, begin to express your ps to Jesus. Feel free to say or write as much as you like. Trust me, He's listening/reading.
ps. Jesus, You are my pollo to my arroz!