Because believing is more than I believe in Jesus as many teach. Its the very first step in the process. Many stop at this first step and never wean themselves from milk to solid food. Sadly, its because that's what most churches teaches. They read one verse in the bible and stop there. The Bible is a Big book for a reason.
If we look at our Bibles, faith comes from hearing Romans 10:17, those with faith believe - they have the faith in Jesus and
of Jesus Rev 14:12 which means believe what He taught and live as He lived for our example 1 John 2:6 , and those with faith DO. James 1:22 Luke 6:46
God knows who are His and who are not. There are wheat and tares. Meaning there are people who seem godly, profess God's name, but they live in their sins never wanting to come to Jesus fully to surrender and forsake their sins - which means turn from Pro28:13 so while they think their are living in light, their are really living in darkness because they do not what to give us their sins John3:19-21 and live the Jesus asked us to. John14:15. Not to be saved, because thats what someone with faith does- Hear His voice and DOES what He asks. Not what we feel is right and wrong which is sadly what most people depend on. Instead of what He deems is righteous (right and wrong doing) Psa 119:172 Isa 56:1-2
Why He tells us what is going to happen at the end of time
Mat 7:21
“Not everyone who says to Me, ‘Lord, Lord,’ shall enter the kingdom of heaven, but he who does the will of My Father in heaven. 22 Many will say to Me in that day, ‘Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?’ 23
And then I will declare to them, ‘I never knew you; depart from Me, you who practice lawlessness!’
1 John 2:3
Now by this we know that we know Him, if we keep His commandments. 4
He who says, “I know Him,” and does not keep His commandments, is a liar, and the truth is not in him. 5
But whoever keeps His word, truly the love of God [a]is perfected in him.
By this we know that we are in Him. 6
He who says he abides in Him ought himself also to walk just as He walked.
Judgement is because God knows who is His or not, many people think they can judge themselves if they are saved or not, but that is clearly for Jesus to decide, and He tells us plainly many believers -those who say Lord Lord will not enter His Kingdom.