Come now, you who say, “Today or tomorrow we shall go into such and such a town, spend a year there doing business, and make a profit”– you have no idea what your life will be like tomorrow. You are a puff of smoke that appears briefly and then disappears. Instead you should say, “If the Lord wills it, we shall live to do this or that.
We forget that God is Being itself. The fact that I exists is because from moment to moment God holds me in being. Jesus tells us:
Apart from me you can do nothing (Jn 15:5)
And that includes existing. Even the person who denies the existence of God is being held in existence by the God they claim does not exist.
St. James reminds us that we are an atmis ( mist, vapor, puff of smoke), that without God would simply vanish into nothingness. We appear briefly in this world and just as quickly we disappear from this world. But where will we disappear to, to eternal life in unity with God, or eternal separation from God.
Will you have a tomorrow? God willing.
So don't waste the now that you do have.