This is the full text of Jane's letter to Katherine, as printed by John Foxe. The Last Tudor will be available on 8th August. It can be ordered here: UK | USA | Canada | Australia & New Zealand

Lady Jane Grey to her sister Lady Katherine Grey (1554)

I Haue here sente you (good sister Katherin) a booke, which although it bee not outwardlye trimmed with golde, yet inwardly it is more worth then precious stones: it is the boke (dere Sister) of the lawe of the Lorde. It is his testament and last wil, which he bequethed vnto vs wretches, which shall lead you to the pathe of eternall ioye: and if you with a good mind read it, and with an earnest minde do folow it, it shal bring you to an immortall and euerlasting life. It wil teache you to liue, and learne you to die. It shal winne you more then you shoulde haue gained by the possession of your wofull fathers lāds. for, as if god had prospered him you shuld haue inherited his lāds: so if you apply diligētly this boke, sekyng to directe your life after it, you shalbe an inheritor of such riches, as nether the couetous shal withdraw from you, neither thefe shal steale, nether yet the mothes corrupt. Desyre with Dauid (good sister) tunderstād the law of the lord your god: liue stil to die, that you (by death) may purchase eternal lyfe. And truste not that the tenderousnes of your age shal lēghthen your life. For as soone (if God call) goeth the yong as the olde: & labour alwayes to learn to die, de e the worlde, denye the deuill, and despise the eshe, and delite your selfe onely in the Lord. Be penitent for your sinnes, and yet despaire not: be strong in faith, & yet presume not, and desire with saint Paule to be dissolued, and to be with Christ, with whom euē in death ther is life. Be like the good seruaunt, & euen at mid night be waking, lest when death commeth and stealeth vpon you like a thefe in the nighte, you be with the euyll seruaunt found sleping, & lefte for lacke of oyle, you be founde like the ue foolish women, and lyke hym that had not on the weddyng garment, and then ye be cast out from the mariage. Reioyce in Christ, as I trust I do. Folow the steppes of your maister Christ, and take vp your crosse, lay your sinnes on his back and alwaies embrace him. And as touching my death, reioyce as I doe (good Sister) that I shal be deliuered of this corruption, and put on incorruption. For I am assured that I shall for losyng of a mortall lyfe, wynne an immortal lyfe, the whiche I praye God graunt you, sende you of his grace to liue in his feare, and to die in the true christian fayth, from the whiche (in Gods name) I exhort you that you neuer swarue, neither for hope of life, nor for feare of death. For if ye wyl deny his truth to lenghthen youre lyfe, God wyll denye you, and yet shorten youre dayes. And if you will cleaue vnto him, he will prolong your dayes to your comforte and hys glory, to the whiche glory god bring me nowe, and you hereafter when it pleaseth hym to call you. Fare you well (good Sister) and put your onely trust in god, who onely muste helpe you.

John Foxe, The Unabridged Acts and Monuments Online or TAMO (1563 edition) (HRI Online Publications, Sheffield, 2011). Available from: http://www.johnfoxe.org