This ought to be a good lesson:

Mt 6:4  ei sijai so armahairtiya yeina in fulhsnja. jah atta yeins saei saiviy in fulhsnja. usgibiy yus in bairhtein.

KJV: That thine alms may be in secret; and thy father which seeth in secret himself shall reward thee openly.

RU: чтобы милостыня твоя была втайне; и Отец твой, видящий тайное, воздаст тебе явно.

ei - we surmised above in lesson 2 that this was somewhat like Latin ut, and this seems to confirm this.  So I am going to conjecture for the moment that sijai is the subjunctive of the verb 'to be' = dass sei, ut sit.

so armahairtiya yeina = the misericordia thine.  Note how neatly I have etymologized a la Junius.  I know a little German, so arm looks like 'poor' (miser) to me (cf. also OE earm), -hairtiya looks like some form of -hairt-, which I take to be the root of the word 'heart', so almsgiving, as in Latin (cf. Mod. Germ. (B)armherzigkeit (Germans are always sticking consonants on, cf. (G)unst 'favor'; (N)atter 'adder' [whoa there!]).

in fulhsnja. What a mouthful!  We know that it is probably in the dative, since we said that in takes the dative.

jah. As an aside, let me note that Junius first spelled this as gah (sounds like Lucy van Pelt) and did not distinguish between j- and g-; Latin having no j- helped him out.

atta has got to be the nominative of the attin (dative) that we saw above. A strange word for father, but cf. Attaturk.  Dare we now propose that Attila (Bavaro-Austrian Etzel) means 'little father'. We adopted the names Medtextl and Gerlingl BTW because we were all Austrians at the time, and could not work in -erl.

yeins must be the possessive adjective, must be masculine.  As Indo- Europeanists (2d Lat. decl.), we figure an -s here is good. Probably the yeina above is feminine.  All sounds so familiar and comfortable.

saei, rel. pronoun, probably masculine, maybe connected with ei above.

saiviy 'seeth'. -iy = -eth, so saiv- is the root for 'to see', as we saw above; thus saivan is the infinitive, also the passive infinitive.

in fulhsnja. Still a mouthful.

usgibiy = outgiveth.  It's alright to twist the English a little now and again. Now we have us- 'out' and gib- 'give'.

yus, as we saw above, this = German dir.

in bairhtein 'openly'.  I opt for metathesis here. It makes no difference, since we are just woofing around, but may as well: 'in brightitude'.

I am beginning to have more sympathy for those who feel they have to make up a new language to be able to translate these old ones (as in the Bibliotheque de la Pleiade Dante).