What did John mean by saying, “Behold the Lamb of God”? Behold, in the Latin, “ecce,” is a note of admiration, of wonderment, of exclamation. “Behold the Lamb of God!” There was nothing of greater wonder ever seen than that God, Himself, should provide the Lamb for the burnt offering, that He should provide His only Son out of His very bosom, that He should give the delight of His heart to die for us! Well may we behold this great wonder! Angels admire and marvel at this mystery of godliness—God manifest in the flesh! They have never left off wondering and adoring the grace of God that gave Jesus to be the sacrifice for guilty men. Behold and wonder, never leave off wondering—tell it as a wonder, think of it as a wonder, sing of it as a wonder! Even in heaven you will not cease to wonder at this glorious Lamb of God!
I think that John also meant his disciples to consider, when he said to them, “Behold the Lamb of God!” So we say to you, “Think of Him, study Him, know all that you can about Him, look Him up and down. He is God—do you understand that He stood in the sinner’s place? He is man—do you know how near akin He is to you, how sympathetic He is—a brother born for your adversity? The person of Christ is a great marvel—how can God and man be in one person? It is impossible for us to tell. We believe what we cannot comprehend and we rejoice in what we cannot understand! He whom God has provided to be your Savior is both God and man—He can lay His hand upon both parties. He can touch your manhood in its weakness and touch the Godhead in its all-sufficiency! Study Christ! The most excellent of all the sciences is the knowledge of a crucified Savior. He is most learned in the university of heaven who knows most of Christ. He who has known most of Him still says that His love surpasses knowledge. Behold Him, then, with wonder! And behold Him with thankfulness. But when John says, “Behold the Lamb of God!” he means more than wondering or considering. “Looking” is used in Scripture for faith—“Look unto Me and be you saved.” Therefore we sing—

“There is life for a look at the crucified One,
There is life at this moment for you!”

Beholding is a steady kind of looking. Believe then, in Christ with a solid, abiding confidence. Come, you sinners, come, and trust your Savior, not for tonight, only, but forever! Believe that He is able and willing to save you and trust Him to do so—

“Venture on Him, venture wholly,
Let no other trust intrude.”

Take your eyes off everything else and behold the Lamb of God! You need not see anything else, nothing else is worth seeing, but behold Him. See how He takes your guilt, see how He bears it, see how He sinks under it and yet rises from it, crying, “It is finished!” He gives up the ghost. He is buried. He rises again from the dead because He is accepted of God and His redeeming work is done. Trust Him, trust Him, trust Him! “Look and live,” is now our message—not, “do and live,” but, “live and do!” If you ask how you are to live, our answer is look, trust, believe, confide, rest in Christ—and the moment you do so, you are saved!

But, once more, when John said to His disciples, “Behold the Lamb of God!” it was a hint that they should leave off looking at John and turn their attention wholly to Jesus and follow Him. Hence we find that John’s two disciples left him and became the disciples of Christ. Beloved, we who preach long to have your attention, but when you give your attention to us, our longing, then, is to pass it on to Christ our Lord. Look on Him and follow Him, not us! What can we do, poor creatures that we are? Look unto Him! Mark His footsteps! Walk in them. Do as He bids you! Take Him for your Lord, become His disciples, His servants. Behold the Lamb of God and always behold Him! Look to Him, look up to Him and follow where He leads the way. — 

Charles Spurgeon