I received several emails from a reader wanting to understand how should in Eph 2:10 is not guaranteed, but it is in John 3:16.
Both passages use a conjunction, hina (that, in order that), plus a verb in the subjunctive mood.
Hina plus the subjunctive expresses purpose or result. The purpose or result is that which is intended. It may or may not be guaranteed. But it is the intended purpose or result.
The fact that hina occurs with a subjunctive doesn’t tell us whether the intended purpose or result is guaranteed or not. That is discovered by studying the context.
In John 3:16 we know the intended result is guaranteed by the context. Two verses later we learn that the one who believes in Him is not condemned. Condemnation is parallel to perishing as a comparision of John 3:16 and 3:17 shows. Thus “should not perish” in 3:16 is guaranteed, not merely possible. Once a person believes, his eternal destiny is secure. This is also evident in the larger context of John 3:16, that is, the whole book. Compare John 1:12-13; 4:10-14; 5:24; 6:35, 37, 39, 45; 11:25-27; 20:31.
In Eph 2:10 the matter is less certain. First, we must note the change from the second person plural, you, in Eph 2:8-9, to the first person plural, we, in Eph 2:10. This is striking. “We” in Ephesians refers to Jews and Gentiles together in one body, the Church. Thus Paul is speaking collectively in Eph 2:10, unlike in John 3:16 where he is speaking individually (”whoever”).
The Church collectively is intended to produce good works that God prepared beforehand. Does she? That is a matter of conjecture. I don’t think Ephesians definitively answers that question, nor the entire NT. Clearly as a group good works always emanate from the Body of Christ on earth. That is to say there are always some good works coming out of some of the local churches on earth each and every generation and indeed each and every day. However, is that what Paul means in Eph 2:10? Since he is writing to the Church of Ephesus, it is likely that he expects them to read this as the intended result for them particularly, as well as for the entire Church collectively. There surely was no guarantee that the Church in Ephesus would remain faithful to Christ. Compare Rev 2:1-7, which had some good deeds coming from it (Rev 2:2-3, 6), but also that church had lost its first love (Rev 2:4-5).
In any case, it is wrong to read Eph 2:10 and think that Paul is guaranteeing that individual believers will produce lives chararacterized by good works, or even with enough good works to show anyone who is looking that these people are clearly different than the unbelievers around them. Compare 1 Cor 3:3 where Paul says that the five-years-in-the-faith believers in Corinth will still walking “like mere men,” that is, like unbelievers.
And it would also be completely wrong to see that hina plus the subjunctive occurs in John 3:16 (and John 3:15) and conclude that the granting of eternal life to the believer is intended, but not guaranteed. The context shows it is guaranteed.
Note too that the two constructions are different. In John 3:16 the hina clause has a condition within it: “that (hina) whoever believes in HIm (condition) should not perish (subjunctive mood) but should have eternal life” (subjunctive mood). In Eph 2:10 there is no condition in the hina clause: “that (hina) we should walk in them” (subjunctive mood). In John 3:16, whoever believes in Him will never perish but has everlasting life. In Eph 2:10 the Church has been created for good works in order that she should walk in them, though individual believers and individual local churches may or may not do so faithfully.