1 Peter 1:13-16
13. Wherefore gird up the loins of your mind, be sober, and hope to the end for the grace that is to be brought unto you at the revelation of Jesus Christ;
13. Quare succincti lumbis mentis vestrae, sobrii, perfecte sperate in eam quae ad vos defertur gratiam, in revelatione Jesu Christi;
14. As obedient children, not fashioning yourselves according to the former lusts in your ignorance:
14. Tanquam filii obedientes, non conformati pristinis, quae in ignorantia vestra regnarunt, cupiditatibus:
15. But as he which hath called you is holy, so be ye holy in all manner of conversation;
15. Sed quaemadmodum is qui vos vocavit sanctus est, ita ipsi sancti in tota conversatione reddamini;
16. Because it is written, Be ye holy; for I am holy.
16. Propterea quòd scriptum est, Sancti estote, quia ego sanctus sum. (Leviticus 11:44; 19:2; 20:7.)
From the greatness and excellency of grace he draws an exhortation, that it surely behoved them the more readily to receive the grace of God, as the more bountifully he bestowed it upon them. And we must notice the connection: he had said, that so elevated was the kingdom of Christ, to which the gospel calls us, that even angels in heaven desire to see it; what then ought to be done by us who are in the world? Doubtless, as long as we live on earth, so great is the distance between us and Christ, that in vain he invites us to himself. It is hence necessary for us to put off the image of Adam and to cast aside the whole world and all hinderances, that being thus set at liberty we may rise upwards to Christ. And he exhorted those to whom he wrote, to be prepared and sober, and to hope for the graces offered to them, and also to renounce the world and their former life, and to be conformed to the will of God. 
Then the first part of the exhortation is, to gird up the loins of their mind and to direct their thoughts to the hope of the grace presented to them. In the second par, he prescribes the manner, that having their minds changed, they were to be formed after the image of God.
13 Wherefore gird up the loins of your mind It is a similitude taken from an ancient custom; for when they had long garments, they could not make a journey, nor conveniently do any work, without being girded up. Hence these expressions, to gird up one's-self for a work or an undertaking. He then bids them to remove all impediments, that being set at liberty they might go on to God. Those who philosophize more refinedly about the loins, as though he commanded lusts to be restrained and checked, depart from the real meaning of the Apostle, for these words mean the same with those of Christ,
"Let your loins be girded about, and burning lamps in your hands," (Luke 12:35,)
except that Peter doubles the metaphor by ascribing loins to the mind. And he intimates that our minds are held entangled by the passing cares of the world and by vain desires, so that they rise not upward to God. Whosoever, then, really wishes to have this hope, let him learn in the first place to disentangle himself from the world, and gird up his mind that it may not turn aside to vain affections. And for the same purpose he enjoins sobriety, which immediately follows; for he commends not temperance only in eating and drinking, but rather spiritual sobriety, when all our thoughts and affections are so kept as not to be inebriated with the allurements of this world. For since even the least taste of them stealthily draws us away from God, when one plunges himself into these, he must necessarily become sleepy and stupid, and he forgets God and the things of God.
Hope to the end, or, Perfectly hope. He intimates that those who let their minds loose on vanity, did not really and sincerely hope for the grace of God; for though they had some hope, yet as they vacillated and were tossed to and fro in the world, there was no solidity in their hope. Then he says, for the grace which will be brought to you, in order that they might be more prompt to receive it. God ought to be sought, though far off; but he comes of his own will to meet us. How great, then, must be our ingratitude if we neglect the grace that is thus set before us! This amplification, then, is especially intended to stimulate our hope.
What he adds, At the revelation of Jesus Christ, may be explained in two ways: that the doctrine of the Gospel reveals Christ to us; and that, as we see him as yet only through a mirror and enigmatically, a full revelation is deferred to the last day. The first meaning is approved by Erasmus, nor do I reject it. The second seems, however, to be more suitable to the passage. For the object of Peter was to call us away beyond the world; for this purpose the fittest thing was the recollection of Christ's coming. For when we direct our eyes to this event, this world becomes crucified to us, and we to the world. Besides, according to this meaning, Peter used the expression shortly before. Nor is it a new thing for the apostles to employ the preposition en in the sense of eis. Thus, then, I explain the passage, — "You have no need to make a long journey that you may attain the grace of God; for God anticipates you; inasmuch as he brings it to you." But as the fruition of it will not be until Christ appears from heaven, in whom is hid the salvation of the godly, there is need, in the meantime, of hope; for the grace of Christ is now offered to us in vain, except we patiently wait until the coming of Christ.
14 As obedient children He first intimates that we are called by the Lord to the privilege and honor of adoption through the Gospel; and, secondly, that we are adopted for this end, that he might have us as his obedient children. For though obedience does not make us children, as the gift of adoption is gratuitous, yet it distinguishes children from aliens. How far, indeed, this obedience extends, Peter shews, when he forbids God's children to conform to or to comply with the desires of this world, and when he exhorts them, on the contrary, to conform to the will of God. The sum of the whole law, and of all that God requires of us, is this, that his image should shine forth in us, so that we should not be degenerate children. But this cannot be except we be renewed and put off the image of old Adam.
Hence we learn what Christians ought to propose to themselves as an object throughout life, that is, to resemble God in holiness and purity. But as all the thoughts and feelings of our flesh are in opposition to God, and the whole bent of our mind is enmity to him, hence Peter begins with the renunciation of the world; and certainly, whenever the Scripture speaks of the renewal of God's image in us, it begins here, that the old man with his lusts is to be destroyed.
In your ignorance The time of ignorance he calls that before they were called into the faith of Christ. We hence learn that unbelief is the fountain of all evils. For he does not use the word ignorance, as we commonly do; for that Platonic dogma is false, that ignorance alone is the cause of sin. But yet, how much soever conscience may reprove the unbelieving, nevertheless they go astray as the blind in darkness, because they know not the right way, and they are without the true light. According to this meaning, Paul says,
"Ye henceforth walk not as the Gentiles, in the vanity of their mind, who have the mind darkened, being alienated from the life of God, because of the ignorance that is in them."
Where the knowledge of God is not, there darkness, error, vanity, destitution of light and life, prevail. These things, however, do not render it impossible that the ungodly should be conscious of doing wrong when they sin, and know that their judge is in heaven, and feel an executioner within them. In short, as the kingdom of God is a kingdom of light, all who are alienated from him must necessarily be blind and go astray in a labyrinth.
We are in the meantime reminded, that we are for this end illuminated as to the knowledge of God, that we may no longer be carried away by roving lusts. Hence, as much progress any one has made in newness of life, so much progress has he made in the knowledge of God.
Here a question arises, — Since he addressed the Jews, who were acquainted with the law, and were brought up in the worship of the only true God, why did he charge them with ignorance and blindness, as though they were heathens? To this I answer, that it hence appears how profitless is all knowledge without Christ. When Paul exposed the vain boasting of those who wished to be wise apart from Christ, he justly said in one short sentence, that they did not hold the head. (Colossians 2:19.) Such were the Jews; being otherwise imbued with numberless corruptions, they had a veil over the eyes, so that they did not see Christ in the Law. The doctrine in which they had been taught was indeed a true light; but they were blind in the midst of light, as long as the Sun of Righteousness was hid to them. But if Peter declares that the literal disciples even of the Law were in darkness like the heathens, as long as they were ignorant of Christ, the only true wisdom of God, with how much greater care it behoves us to strive for the knowledge of him!
15 He who hath called you is holy He reasons from the end for which we are called. God sets us apart as a peculiar people for himself; then we ought to be free from all pollutions. And he quotes a sentence which had been often repeated by Moses. For as the people of Israel were on every side surrounded by heathens, from whom they might have easily adopted the worst examples and innumerable corruptions, the Lord frequently recalled them to himself, as though he had said, "Ye have to do with me, ye are mine; then abstain from the pollutions of the Gentiles." We are too ready to look to men, so as to follow their common way of living. Thus it happens, that some lead others in troops to all kinds of evil, until the Lord by his calling separates them.
In bidding us to be holy like himself, the proportion is not that of equals; but we ought to advance in this direction as far as our condition will bear. And as even the most perfect are always very far from coming up to the mark, we ought daily to strive more and more. And we ought to remember that we are not only told what our duty is, but that God also adds, "I am he who sanctify you."
It is added, In all manner of conversation, or, in your whole conduct. There is then no part of our life which is not to be redolent with this good odour of holiness. For we see that in the smallest things and almost insignificant, the Lord accustomed his people to the practice of holiness, in order that they might exercise a more diligent care as to themselves.
 Pareus observes, that the Apostle, in this part of the chapter, exhorted the faithful to sobriety, holiness, humility, and brotherly love, by five reasons: 1, because they were the children of God, ver. 14; 2, because God is holy, and requires holiness, ver. 15; 3, because God is no respecter of persons, ver. 17; 4, because of the value of the price for their redemption, ver. 18; and 5, because they had been born again of an immortal seed, ver. 23. -- Ed.