What it is to fulfil the law perfectly
Thesis XV. To fulfil the law perfectly is to satisfy it in every respect and in all its rigour, falling short in nothing that the law, strictly taken, requires of a person. Such a person could then reach life by virtue of the legal covenant, under its clause 'Do this and you will live', and claim as his right the happiness the law promises, with no fear of the penalties it threatens against those who break it.
No one fulfils the law in that sense and in that respect except someone entirely free of sin who has never broken it. All who have sinned even once are judged, condemned and handed over to the curse by the law strictly taken, under its other, terrible clause: 'Cursed is everyone who does not continue in all the things written in the book of this law, to do them.'
The law justifies and acquits no one freely, but only as a matter of debt, as Paul teaches in Romans 4. Every sinner, whoever he is, needs God's grace and mercy and can be justified only freely.
Latin
XV. Nam perfecte legem implere est omni ex parte legi satisfacere, secundum totum illius rigorem, nec deficere in ullo eorum, quae lex praecise sumpta ab homine postulat, ut possit vi foederis legalis, juxta Clausulam Fac & vives, ad vitam pervenire, & foelicitatem quam lex pollicetur pro jure suo exigere, absque ullo metu poenarum quas lex comminatur praevaricatoribus. Nemo autem eo sensu & respectu legem implet, nisi qui prorsus immunis est a peccato, nec unquam legem transgressus est. Omnes enim qui vel semel peccaverunt, lex rigide sumpta judicat & damnat, & addicit maledictioni, juxta alteram istam terribilem Clausulam, Maledictus omnis qui non permanserit in omnibus quae scripta sunt in libro legis hujus ad faciendum ea. Quippe lex neminem gratis justificat & absolvit, sed tantum ex debito, secundum Pauli doctrinam, Rom. 4. Omnis peccator autem, quicunque tandem ille sit, eget Dei gratia & misericordia, nec nisi gratis justificari potest.