Whoso walketh uprightly shall be saved. "Uprightly" (tamim); innocently, blamelessly (Psalms 15:2). Vulgate, simpliciter; Septuagint, δικαίως; Aquila, Symmachus, τέλειος. "He is helped ( βεβοήθηται)," Septuagint. Things shall prosper with him; God will work with him, and save him in dangers temporal and spiritual. But he that is perverse in his ways shall fall at once. "He that is perverse of two ways," or "in a double way," as Proverbs 28:6. The man who is not straightforward, but vacillates between right and wrong, or pretends to be pursuing one path while he is really taking another, shall fall suddenly and without warning. בְּאֶחָת means "all at once," or "once for all," and so that nothing else is possible, equivalent to penitus. Schultens quotes Virgil, 'AEneid,' 11.418—
"Procubuit moriens et humum semel ore momordit."
Septuagint, "He that walketh in crooked ways will be entangled."