To MGVH: I didn't mean to say that Leedy or OpenText was "abysmal"; I meant to say that about the syntax of 1 John 3:19-20. (No disrespect or irreverence intended; it's just that, as anyone who has studied it agrees, it is "a mess.")
To MBushell: In my haste, I overlooked the Passage Notes in Leedy. Quite impressively detailed; thanks! I tend to agree with BW's reasoning regarding including syntactical databases. What's there in Leedy and MacDonald should be enough for most users to follow most sentences; and experts will want to approach the text without extra lenses.
FWIW, this is what I wrote in my Abingdon NT Commentary on 1, 2, and 3 John:
First John 3:19-20 is one of the most obscure sentences in the New Testament.... The verb peisomen should mean “we shall convince”; but commentators often cite evidence for “we shall pacify” or “reassure” (NRSV). In the following clauses we find hoti (either “that” or “because”), ean (normally “if”), and another hoti. It is the presence of two hotis that lies at the root of the problem.... Translated literally, and with all the ambiguities displayed, the Greek runs, “In this we shall know that we are of the truth, and before him we shall convince/reassure our heart that/because, if the heart condemns us, that/because God is greater than our heart and knows everything.”
The most common solution is to translate peisomen “reassure”; to reinterpret hoti ean as ho ti an, “in whatever case, whenever”; and to translate the second hoti “because” or “for” (e.g, NRSV, NIV, NAB, REB; Brooke 1912, 100; Marshall 1978, 197 n. 4; Schnackenburg 1992, 185). However, the evidence that peisomen can mean “reassure” is weak, as is the evidence for this adverbial usage of ho ti an (which is also in the wrong case to be the object of “condemn” [Boyer 1988, 254]). Some, therefore, consider the second hoti redundant, either as simply resuming the first or as a grammatical error. This yields either “we shall reassure our heart because, if our heart condemns us, God is greater...” (cf. the KJV); or (more naturally) “we shall convince our heart that, if our heart condemns us, God is greater...” (cf. the NEB; and see, e.g., Houlden 1973, 102; Brown 1982, 457-458. First John does not use a resumptive hoti in comparable passages elsewhere (3:2; 5:14); however, it seems more plausible that the author has violated his usual practice in this regard than that he has created virtually unparalleled usages of peisomen and ho ti an. The translation adopted by Houlden, Brown, and others is probably correct.
This seems similar to Leedy's approach. Personally, I think that the writer simply got lost in his own sentence and added a second hoti ungrammatically, as people sometimes say in English, "I told her that if I came by that I would bring a cake." 1 and 2 John have a number of difficult sentences like this.
Recent translations don't offer much advance on this. The translators of the NET Bible are to be commended for courage, if nothing else, for translating all of the hotis as "that" (and for the detail of their notes): "And by this we will know that we are of the truth and will convince our conscience in his presence, 20 that if our conscience condemns us, that God is greater than our conscience and knows all things."
Well, sorry for the topic drift! I, at any rate, have learned something new about tools available in BW.