In addition to all these, there are ups and downs of our own nature, the fluctuations which are sure to occur in any human heart, when faith seems to ebb and falter, and love to die down almost into cold ashes. But, dear brethren, whilst we shall always be liable to these fluctuations of feeling, it is possible for us to have, deep down below these, a central core of our personality, in which unchanging continuity may abide. The depths of the ocean know nothing of the tides on the surface that are due to the mutable moon. We can have in our inmost hearts steadfastness, immovableness, even though the surface may be ruffled. Make your spirits like one of those great cathedrals whose thick walls keep out the noises of the world, and in whose still equability there is neither excessive heat nor excessive cold, but an approximately uniform temperature, at midsummer and at midwinter. 'Stand fast in the Lord.' Now, my text not only gives an exhortation, but, in the very act of giving it, suggests how it is to be fulfilled. For that phrase 'in the Lord' not only indicates _where_ we are to stand, but also _how_. That is to say--it is only in proportion as we keep ourselves in union with Christ, in heart and mind, and will, and work, that we shall stand steadfast. The lightest substances may be made stable, if they are glued on to something stable. You can mortice a bit of thin stone into the living rock, and then it will stand 'four-square to every wind that blows.' So it is only on condition of our keeping ourselves in Jesus Christ, that we are able to keep ourselves steadfast, and to present a front of resistance that does not yield one foot, either to imperceptible continuous pressure, to sudden assaults, or to the fluctuations of our own changeful dispositions and tempers. The ground on which a man stands has a great deal to do with the firmness of his footing. You cannot stand fast upon a bed of slime, or upon a sand-bank which is being undermined by the tides. And if we, changeful creatures, are to be steadfast in any region, our surest way of being so is to knit ourselves to Him 'who is the same yesterday, and to-day, and for ever,' and from whose immortality will flow some copy and reflection of itself into our else changeful natures.