Romans 3:23 — For all have sinned and fallen short of the glory of God;

You know the song …

You better watch out
you better not cry
you better not pout
I’m telling you why
Santa Claus is coming to town
He’s making a list
And checking it twice
Gonna find out who’s naughty or nice
Santa Claus is coming to town

Santa’s rules: Every year you get a reset. Start from scratch, and the balance of naughty and nice will determine whether you get gifts under the tree or a lump of coal in your stocking. I wonder what age you were when you figured out that the world doesn’t work like that?
God’s economy, of course, is different. Would it surprise you to know that He has a list too? It’s called the “Book of Life” and the “Lamb’s Book of life”. The terms refer to the same thing — it is the list of those who are destined for eternal life, rather than an eternity in the lake of fire. There’s a few things we need to know about the Book of Life:
How does God make His list? Santa checks his list to see if you’ve been naughty or nice. The fancy theological term for that is he looks at your works. God doesn’t do it that way. He checks your faith. “For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.” (Ephesians 2:8-9). At its simplest it comes down to believing in Jesus. Going just a little bit more deeply, it involves admitting that — just like everyone else you are a sinner, believing that Jesus paid the penalty for those sins and accepting Him as your Lord. Do that, and you’re on the list.
God’s list never resets! “For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.” (John 3:16) “For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come, Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord.” (Romans 8:38-39)
Oh … and like Santa, God coming to town! But nobody knows quite when, for as Jesus told his disciples: “But of that day and hour knoweth no man, no, not the angels of heaven, but my Father only. … Watch therefore: for ye know not what hour your Lord doth come. … Therefore be ye also ready: for in such an hour as ye think not the Son of man cometh.” (Matthew 24:36, 42, 44)
So, if you’re not on the list, not in the Book of Life … “You better watch out” … because you don’t know when the Lord is coming.