The normal way to express the idea of present tense obligation in Russian is with должен. If one wanted to say 'he should speak', one could say 'он должен сказать'. But должен (and other options, including вынужден, Нужно, and Надо (and Необходимоб?)) are all adjectives, but even though the copular verb is typically left out in predicate adjective sentences, these adjectives are interpreted as if there were a finite copular verb present (he IS obligated, etc). I am not sure that Wiktionary is acceptable to quote here, but it says of должен: "Grammatically, this term is an adjective that has only short forms, but it is best translated as a verb, either ought to/must/have (has) to if followed by an infinitive, or owe(s) if followed by a direct and indirect object.'
I would be open to using должен if one wanted to communicate the idea of obligation if the subject is not God. Thus, for 'Paul should speak', I would be open to using 'Пол должен сказать', but due to religious conviction, I am not willing to use God's name with only an adjective that is not a proper finite present tense verb form, even if the adjective is a predicate adjective. Accordingly, for 'God should speak', I am not willing to use '*ог должен сказать'. I would be willing to use 'бог есть должен сказать' because that has an explicit present tense verb form, but including the есть in cases of a predicate adjective would usually be considered poor or incorrect Russian. I am willing to do that if the subject is God (as I don't want to use his name without an explicit verb, even though predicate adjectives in Russian are treated as if an explicit verb were present), but fortunately, I can also use является in some cases, and I have used some form of являться in certain case(s).
But I have run into a bigger problem in regard to (the lack of?) a present tense verb form for 'should'. I want a present tense auxiliary verb form to use with almost any main verb that would be in the infinitive. But I have communicated with both a proofreader from Belarus and someone from Russia, and they both have left me with the impression that Russian has no such verb. Returning to Wiktionary, its second note has 'In modern Russian, the full infinitive form долженствова́ть (dolženstvovátʹ, literally “to be required to/to be obliged to”) is seldom used.', and both speakers did not approve of that. In Russian it is acceptable to use the future form of быть with должен, such that the text for 'he will have to speak' or 'he will have an obligation to speak' could be 'он должен будет сказать', so I inquired about using the present tense verb form. Would он должен есть сказать work? The present tense есть form of быть is usually avoided, but I still asked, and neither thought this was good. I inquired about a lot of other options. I just want to be able to say 'God must do something' or 'God should do something' with a present tense verb form (which должен is not, even though it is interpreted as such).
- он Обяжет сказать(/любить/прийти/etc)
- он долженствует сказать
- он должен есть сказать
- он является должен сказать
- он находится должен сказать
- он имеется должен сказать
- он существует должен сказать
- он уществует должен сказать
None of these were given a stamp of approval. The native Russian speaker did put out 'ему следует сказать', so it seems that, if I wanted to translate the English [SUBJECT] [SHOULD] [FILL-IN-THE-VERB], I could use in Russian, [ENGLISH SUBJECT IN DATIVE FORM] + следует + [RUSSIAN-VERB-IN-THE-INFINITIVE]. But that would require converting the English subject into dative form. I want to have the doer of the action be in the nominative form in Russian, a word or words for 'should' that function in an auxiliary capacity (one of which is a present tense verb form), and then a Russian verb in the infinitive for the action that the subject should do. Is there any word in Russian that can do this that would be acceptable? Or if not, is there a present tense verb form (or phrase that has a present tense verb form) that I can use that Russians would understand as meaning 'should do [fill-in-the-verb]', even if it is considered poor Russian?