A common critique from a secular perspective of certain formulations of Christianity is essentially a variation of the idea that ‘a bird in the hand is worth two in the bush’.
So, the critic argues, since there are good things here and now that are well-evidenced, this is worth more than things that are put forth as possible future goods in standard Christianity in some sort of Paradise or Heaven.
How is a Christian to respond? I think there are two major points to be made.
1. If one ‘lets go of the bird in the hand’, so to speak, along the lines that are often advocated within Christian practice, one can find that multiple birds return or perch anew on one’s hand (love, inner peace, joy, and so on). That this occurs in many cases seems obvious, and in such cases a giving up of various things isn’t actually a giving up. Once God is put in first place (a typical Christian idea goes), a large number of other good things will be added typically in the here and now.
2. Having said that, the evidence that one can obtain the ‘two birds in the bush’ later on is stronger than is often thought. That is, the lines of evidence which converge on some sort of continued existence, where the goods that can be obtained there far exceed the goods here and now are multiple.
The first and central line of evidence is the experience many Christians have, after which they are left with a feeling that they know there is a Heaven, and that one can get to it. That is, it seems that they perceive or have knowledge of something which corresponds to some degree to the Christian notions of God and Heaven. The witnesses are many and, in most cases, credible in other aspects (doctors, architects, teachers, and so on).
Another line of evidence is in the many people who have died, and then reported something like the Christian Paradise or Heaven* upon resuscitation.
* I would argue that Paradise should be used for the immediate state a subjective self enters into, which is a sort of closeness to God, whereas Heaven should be used for the resurrected, fully bodily state (as N.T. Wright refers to it, the ‘Heaven after Heaven’) that Christianity holds will obtain at some future time. Be that as it may, Heaven in popular vernacular is used to refer to the immediate state a subjective self or soul enters into.
A third line of evidence is considerations on the nature of the continuity of the subjective self (for example, we say a person has the same basic subjective self at time 1 and time 2, where the matter of which their bodies is composed has changed, and the form of that matter has also changed – therefore, neither the stuff of which they are made nor the particular formation of it can account for the continuity of their subjective self).