2. _This duty is also enforced by the analogy of the visible creation._ The most complete and perfect system, order, and harmony, may be read in every page of the book of nature. From the minutest insect, up through all the animal creation, to the structure of our own bodies, there is a systematic arrangement of every particle of matter. So, from the little pebble that is washed upon the sea-shore, up to the loftiest worlds, and the whole planetary system, the same truth is manifest. 3. _This duty is enforced by our obligation to employ all our time for the glory of God._ If we neglect the systematic arrangement of all our affairs, we lose much precious time, which might have been employed in the service of the Lord. I shall close this letter with a few remarks upon the nature of obligation. The very idea of obligation supposes the possibility of the thing being done that is required. There can be no such thing as our being under obligation to do what is in its own nature impossible. The idea itself is absurd. This principle is recognized by our Lord in the parable of the talents. The man only required of his servants _according to their ability_. Nothing, then, is duty except what can be done at the present moment. There are other things which may be duty hereafter; but they are not _present duty_. Now, the great principle which I would here establish is, as I have elsewhere remarked, that the _obligation of duty rests upon the present moment_. No principle can be of greater importance in practical life than this. It lies at the foundation of all Christian effort. It is the neglect of it which has ruined thousands of immortal souls, who have sat under the sound of the gospel. It is the neglect of it which keeps the church so low. If it is the duty of a sinner to repent, it is his duty to do it _now_; and every moment's delay is a new act of rebellion against God. If it is the duty of a backslider to return and humble himself before God, it is his duty to do it _now_; and every moment he delays, he is going farther from God, and rendering his return more difficult. If it is the duty of a Christian to live near to God; to feel his presence; to hold communion with him; to be affected with the infinite beauty and excellence of his holy character; the obligation of that duty rests upon the present moment. Every moment's delay is _sin_. And so of every other duty. Our first object, then, is to _know_ present duty; our second, to _do_ it. We cannot put off anything which we ought to do _now_, without bringing guilt upon our Souls. Your affectionate Brother. LETTER XIII. _Christian Activity._ "She hath done what she could."--MARK 14:8. MY DEAR SISTER,