The birth of Isaac did not improve Ishmael, but only brought out his real opposition to the child of promise. He might have gone on very quietly and orderly till Isaac made his appearance; but then he showed what he was by persecuting and mocking at the child of resurrection. What, then, was the remedy? To make Ishmael better? By no means; but, "cast out this bond-woman and her son; for the son of this bond-woman shall not be heir with my son, even with Isaac." (8-10.) Here was the only remedy. "That which is crooked cannot be made straight;" therefore you have only to get rid of the crooked thing altogether, and occupy yourself with that which is divinely straight. It is labor lost to seek to make a crooked thing straight. Hence all efforts after the improvement of nature are utterly futile, so far as God is concerned. It may be all very well for men to cultivate and improve that which is of use to themselves; but God has given his children something infinitely better to do, even to cultivate that which is his own creation, the fruits of which, while they in no wise serve to exalt nature, are entirely to his praise and glory. Now, the error into which the Galatian churches fell, was the introduction of that which addressed itself to nature. "Except ye be circumcised after the manner of Moses, ye cannot be saved." Here salvation was made to depend upon something that man could be, or man could do, or man could keep. This was upsetting the whole glorious fabric of redemption, which, as the believer knows, rests exclusively upon what Christ is, and what he has done. To make salvation dependent in the most remote manner upon any thing in, or done by, man, is to set it entirely aside. In other words, Ishmael must be entirely cast out, and all Abraham's hopes be made to depend upon what God had done and given in the person of Isaac. This, it is needless to say, leaves man nothing to glory in. If present or future blessedness were made to depend upon even a divine change wrought in nature, flesh might glory. Though my nature were improved, it would be something of _me_, and thus God would not have _all_ the glory. But when I am introduced into a new creation, I find it is all of God, designed, matured, developed by himself alone. God is the actor, and I am a worshipper; he is the blesser, and I am the blessed; he is "the better," and I am "the less;" (Heb. vii. 7;) he is the giver, and I am the receiver. This is what makes Christianity what it is; and, moreover, distinguishes it from every system of human religion under the sun, whether it be Romanism, Puseyism, or any other _ism_ whatsoever. Human religion gives the creature a place more or less; it keeps the bond-woman and her son in the house; it gives man something to glory in. On the contrary, Christianity excludes the creature from all interference in the work of salvation; casts out the bond-woman and her son, and gives _all_ the glory to him to whom alone it is due.