As reported here, Michael Horton wrote: "Third, Christ’s work on the cross was not an object lesson." Horton is wrong. Horton would have been right if Horton had said, "The cross was not just an object lesson," but that's not what he wrote.
It is an object lesson here:
1 John 3:16-17
Hereby perceive we the love of God, because he laid down his life for us: and we ought to lay down our lives for the brethren. But whoso hath this world's good, and seeth his brother have need, and shutteth up his bowels of compassion from him, how dwelleth the love of God in him?
Notice that Christ's willingness to sacrifice himself in love for us is given as a moral example here for us to be willing to lay down our own lives for the brethren. It is plainly stated and virtually undeniable.
And Christ's work (though not the cross itself) is an object lesson here:
2 Corinthians 8:3-15
For to their power, I bear record, yea, and beyond their power they were willing of themselves; praying us with much intreaty that we would receive the gift, and take upon us the fellowship of the ministering to the saints. And this they did, not as we hoped, but first gave their own selves to the Lord, and unto us by the will of God. Insomuch that we desired Titus, that as he had begun, so he would also finish in you the same grace also. Therefore, as ye abound in every thing, in faith, and utterance, and knowledge, and in all diligence, and in your love to us, see that ye abound in this grace also. I speak not by commandment, but by occasion of the forwardness of others, and to prove the sincerity of your love. For ye know the grace of our Lord Jesus Christ, that, though he was rich, yet for your sakes he became poor, that ye through his poverty might be rich. And herein I give my advice: for this is expedient for you, who have begun before, not only to do, but also to be forward a year ago. Now therefore perform the doing of it; that as there was a readiness to will, so there may be a performance also out of that which ye have. For if there be first a willing mind, it is accepted according to that a man hath, and not according to that he hath not. For I mean not that other men be eased, and ye burdened: but by an equality, that now at this time your abundance may be a supply for their want, that their abundance also may be a supply for your want: that there may be equality: as it is written, He that had gathered much had nothing over; and he that had gathered little had no lack.
The lesson here is similar the previous lesson.
It's perfectly fine for people to say that Christ's earthly ministry (and particularly the cross) are not merely an object lesson. But it is contrary to Scripture to deny that the cross is an object lesson. Horton ought to affirm the truths that he does affirm about the cross (that it was a sacrifice to satisfy divine justice) without denying the other truths as well.
Some more examples of the cross an object lesson or moral example:
Matthew 16:24 Then said Jesus unto his disciples, If any man will come after me, let him deny himself, and take up his cross, and follow me.
Mark 8:34 And when he had called the people unto him with his disciples also, he said unto them, Whosoever will come after me, let him deny himself, and take up his cross, and follow me.
Mark 10:21 Then Jesus beholding him loved him, and said unto him, One thing thou lackest: go thy way, sell whatsoever thou hast, and give to the poor, and thou shalt have treasure in heaven: and come, take up the cross, and follow me.