Politicians, commercials, sports stars and others all make promises on which they fail to deliver. Many parents, teachers and governments issue threats that they never carry out.
There's a verse in the Bible that contains a promise and a threat, and these are things you can bank on, they aren't empty.
John 3 v 36 says
He who believes in the Son has everlasting life; and he who does not believe the Son shall not see life, but the wrath of God abides on him.Notice the promise - He who believes in the Son (that is, the person who depends on the Son of God to save them) has everlasting life. We know this promise is not empty is because it comes from the God who cannot lie (Titus 1 v 2), and depends on a Saviour who cannot fail (Hebrews 7 v 25). There is a living, loving Saviour who is able to save because of His sacrificial death and glorious resurrection, and those who own their guilt and helplessness and trust the Lord to save them will receive everlasting life. An additional reason we know it's not an empty promise is because the Lord actually delivers on it here and now! The verse doesn't say that the person who believes in the Son will be in heaven when they die. The verse says that upon believing the person has everlasting life - they receive new life, a life with new power and new desires. We know the promise is true because we have this new life. By the way, only the Christian Gospel offers this instantaneous and permanent change.
But notice too the threat - He who does not believe the Son shall not see life but the wrath of God abides on him. If you refuse to turn to and trust in the Son of God to save you then you remain exposed to His righteous wrath against your sins. This is not an empty threat, the character of God demands that your sins be paid for, and if you don't accept the payment provided by Christ's death then you'll pay, and you will realise that it was no empty threat.
The Lord is as good as His word, if you trust Him you will receive everlasting life; if you don't, you will receive everlasting wrath.