A comparison with a man who is trying to hit a mark.
As those, whose business it is to use weapons of war, whenever they want to show their skill in their art before a king of this world, try to shoot their arrows or darts into certain small targets which have the prizes painted on them; for they know that they cannot in any other way than by the line of their aim secure the end and the prize they hope for, which they will only then enjoy when they have been able to hit the mark set before them; but if it happens to be withdrawn from their sight, however much in their want of skill their aim may vainly deviate from the straight path, yet they cannot perceive that they have strayed from the direction of the intended straight line because they have no distinct mark to prove the skilfulness of their aim, or to show up its badness: and therefore while they shoot their missiles idly into space, they cannot see how they have gone wrong or how utterly at fault they are, since no mark is their accuser, showing how far they have gone astray from the right direction; nor can an unsteady look help them to correct and restore the straight line enjoined on them. So then the end indeed which we have set before us is, as the Apostle says, eternal life, as he declares, “having indeed your fruit unto holiness, and the end eternal life;” 1088 but the immediate goal is purity of heart, which he not unfairly terms “sanctification,” without which the afore-mentioned end cannot be gained; as if he had said in other words, having your immediate goal in purity of heart, but the end p. 297 life eternal. Of which goal the same blessed Apostle teaches us, and significantly uses the very term, i.e., σκοπός, saying as follows, “Forgetting those things which are behind and reaching forward to those that are before, I press toward the mark, for the prize of the high calling of the Lord:” 1089 which is more clearly put in Greek κατὰ σκοπὸν διώκω, i.e., “I press toward the mark,” as if he said, “With this aim, with which I forget those things that are behind, i.e., the faults of earlier life, I strive to reach as the end the heavenly prize.” Whatever then can help to guide us to this object; viz., purity of heart, we must follow with all our might, but whatever hinders us from it, we must shun as a dangerous and hurtful thing. For, for this we do and endure all things, for this we make light of our kinsfolk, our country, honours, riches, the delights of this world, and all kinds of pleasures, namely in order that we may retain a lasting purity of heart. And so when this object is set before us, we shall always direct our actions and thoughts straight towards the attainment of it; for if it be not constantly fixed before our eyes, it will not only make all our toils vain and useless, and force them to be endured to no purpose and without any reward, but it will also excite all kinds of thoughts opposed to one another. For the mind, which has no fixed point to which it may return, and on which it may chiefly fasten, is sure to rove about from hour to hour and minute to minute in all sorts of wandering thoughts, and from those things which come to it from outside, to be constantly changed into that state which first offers itself to it.
Phil. 3:13, 14.