Jamieson, Fausset and Brown on Matthew 25:9

9. But the wise answered, Not so; lest there be not enough for us and you--The words "Not so," it will be seen, are not in the original, where the reply is very elliptical--"In case there be not enough for us and you." A truly wise answer this. "And what, then, if we shall share it with you? Why, both will be undone."

but go ye rather to them that sell, and buy for yourselves--Here again it would be straining the parable beyond its legitimate design to make it teach that men may get salvation even after they are supposed and required to have it already gotten. It is merely a friendly way of reminding them of the proper way of obtaining the needed and precious article, with a certain reflection on them for having it now to seek. Also, when the parable speaks of "selling" and "buying" that valuable article, it means simply, "Go, get it in the only legitimate way." And yet the word "buy" is significant; for we are elsewhere bidden, "buy wine and milk without money and without price," and "buy of Christ gold tried in the fire," &c. (Is 55:1; Re 3:18). Now, since what we pay the demanded price for becomes thereby our own property, the salvation which we thus take gratuitously at God's hands, being bought in His own sense of that word, becomes ours thereby in inalienable possession. (Compare for the language, Pr 23:23; Mt 13:44).