70 Jesus tells the disciples that he has told them all these things before they happen, so that when they do happen the disciples may believe. This does not mean they had not believed prior to this time; over and over the author has affirmed that they have (cf. 2:11). But when they see these things happen, their level of trust in Jesus will increase and their concept of who he is will expand. The confession of Thomas in 20:28 is representative of this increased understanding of who Jesus is. Cf. John 13:19.

In other versions

And now I have told you before it takes place, so that when it does take place you may believe.

I have told you now before it happens, so that when it does happen you will believe.

I have told you now before it happens so that when it does happen you may believe.

I have told you these things before they happen so that when they do happen, you will believe.

And now I have told you before it happens, so that when it happens, you may believe.

And now I have told you before it come to pass, that, when it is come to pass, ye might believe.

Public Domain