Yohanes 3:12

3:12 If I have told you people ¹  about earthly things and you don’t believe, how will you believe if I tell you about heavenly things? ² 

Yohanes 4:41

4:41 and because of his word many more ³  believed.

Yohanes 12:39

12:39 For this reason they could not believe, ⁴  because again Isaiah said,

[3:12]  ¹ tn The word “people” is not in the Greek text, but is supplied to indicate that the verb is second person plural (referring to more than Nicodemus alone).

[3:12]  ² sn Obviously earthly things and heavenly things are in contrast, but what is the contrast? What are earthly things which Jesus has just spoken to Nicodemus? And through him to others – this is not the first instance of the plural pronoun, see v. 7, you must all. Since Nicodemus began with a plural (we know, v. 2) Jesus continues it, and through Nicodemus addresses a broader audience. It makes most sense to take this as a reference to the things Jesus has just said (and the things he is about to say, vv. 13-15). If this is the case (and it seems the most natural explanation) then earthly things are not necessarily strictly physical things, but are so called because they take place on earth, in contrast to things like v. 16, which take place in heaven. Some have added the suggestion that the things are called earthly because physical analogies (birth, wind, water) are used to describe them. This is possible, but it seems more probable that Jesus calls these things earthly because they happen on earth (even though they are spiritual things). In the context, taking earthly things as referring to the words Jesus has just spoken fits with the fact that Nicodemus did not believe. And he would not after hearing heavenly things either, unless he first believed in the earthly things – which included the necessity of a regenerating work from above, by the Holy Spirit.

[4:41]  ³ tn Or “and they believed much more.”

[12:39]  ⁴ sn The author explicitly states here that Jesus’ Jewish opponents could not believe, and quotes Isa 6:10 to show that God had in fact blinded their eyes and hardened their heart. This OT passage was used elsewhere in the NT to explain Jewish unbelief: Paul’s final words in Acts (28:26-27) are a quotation of this same passage, which he uses to explain why the Jewish people have not accepted the gospel he has preached. A similar passage (Isa 29:10) is quoted in a similar context in Rom 11:8.