Efficacious of itself: infallibly, insuperably, indeclinably
Thesis XXXVII. That is why they call this grace efficacious of itself, that is, grace that by its own force moves and determines free choice, and does so, in their own words, 'infallibly, insuperably, indeclinably'. For the human will cannot cheat it of its effect or prevent it from accomplishing what God properly gives it for, because this divine grace overcomes all human resistance, and its power consists in making a person willing who was unwilling.
Latin
XXXVII. Inde est quod gratiam illam dicunt esse efficacem per se, id est, talem quae vi sua movet & determinat liberum arbitrium: idque, ut ipsi loquuntur, infallibiliter, insuperabiliter, indeclinabiliter: quoniam fieri non potest ut voluntas humana illam effectu suo frustretur, obstetque ne praestet illud ad quod proprie a Deo donatur; propterea quod haec divina gratia omnem hominis resistentiam vincit, & vis ejus in eo consistit, ut homo fiat ex nolente volens.