Do people go to heaven immediately when they die? When someone passes away, at their funeral the priest will usually say something that gives the idea that the deceased is in heaven. And a lot of people also like to give the idea that people who die are with Jesus Christ. For instance, say someone close to you passed away, chances are you've said something that gives the idea that the person is in heaven, such as, "I know you are in a better place, near Jesus Christ."

The reason I ask this question is that the when people die, I know that they go to the world of the dead till the day that Jesus Christ will return. But if people are already in heaven this means that there really isn't much reason for Jesus Christ to return, because all those that believe in Him are already in heaven.

If Jesus Christ will return and all those that have faith in Him will be raised and be priests with Him for a thousand years, why make it seem as if the deceased are already in heaven? If someone dies and goes to heaven before the Last Judgement, what need is there for him to be judged at the final judgement? Hasn't he already been judged righteous if he is in heaven?
That death and "sleeping," are often conflated in Scripture is perhaps a useful metaphor here. Notice how, in 1 Corinthians 15, Paul likens those who have died to those who have "fallen asleep in Christ."


  And if Christ has not been raised, your faith is futile; you are still in your sins. 18 Then those also who have fallen asleep in Christ are lost. 19 If only for this life we have hope in Christ, we are of all people most to be pitied. 20 But Christ has indeed been raised from the dead, the firstfruits of those who have fallen asleep.


This is a useful metaphor, for when a normal person falls asleep, they are unaware of the passage of time.  Whether or not there is a time lag between dying and being raised back up is, in fact, irrelevant.


The person who has died is unaware of the passage of time.  For that person, whether Christ tarries a thousand years or only minutes, is, to the dead, indistinguishable.  There is no sensation between now and then, so it doesn't really matter.
To the person who is still alive, there is no communication in any event, so that the precise location of the soul is not important.  We thus do not "mourn as the Gentiles do," but rather we have a hope and a peace that passes understanding - because we know that at the end of our temporal existence, we will be reunited with our loved ones.  Once we die, sensation ceases for us as well - and at that point, eternity begins. 
To God, who is outside of time, time and space are irrelevant.  All things occur at once.


The next communication we have with our loved ones will, in fact, be in heaven - so in a sense to say they "are in heaven" - which may or may not, at that exact moment, be temporally accurate or not - is not really the question being addressed.  That our next moment of contact will be in heaven is the point, and on that point, if it is not true, then everything else is vain any way. 

In any event, the focus is that at some point, the promise of the Christian life is the hope that we will be resurrected - that we will be "awoken" is beyond doubt - and when we are, oh what a day of rejoicing that will be!


  50 I declare to you, brothers and sisters, that flesh and blood cannot inherit the kingdom of God, nor does the perishable inherit the imperishable. 51 Listen, I tell you a mystery: We will not all sleep, but we will all be changed— 52 in a flash, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, the dead will be raised imperishable, and we will be changed. 


Put another, the current chronology is irrelevant.  The end state is the same - we will all, at some point, in an instant, be together in heaven with Christ.