I Yahweh am its keeper; I will water it every moment: lest any hurt it, I will keep it night and day. — Isaiah 27:3
I give eternal life to them. They will never perish, and no one will snatch them out of my hand. — John 10:28

Author
Charles Spurgeon
Summary: Our eternal security rests in Christ: we belong to Him because He bought us with His blood and received us from the Father. He gives us eternal life; if it could end, it would not be eternal. His promise, “They shall never perish,” assures us that believers will not perish. Moreover, we are in His hand, from which no enemy can snatch us, for our Savior is omnipotent. Therefore, we must cast aside both fleshly fear and fleshly confidence, and rest peacefully in the Redeemer’s hand.
We believe in the eternal security of the saints. First, because they belong to Christ, and He will never lose the sheep He has bought with His blood and received from His Father.
Next, because He gives them eternal life, and if it is eternal, well, then it is eternal, and there can be no end to that life unless there can be an end to hell, to heaven, and to God. If spiritual life could be extinguished, then it would plainly not be eternal life, but temporary life. But the Lord speaks of eternal life, and that effectively rules out the possibility of an end.
Observe, moreover, that the Lord says expressly: “They shall never perish.” As long as words have meaning, this assures believers that they shall not perish. The most obstinate unbelief cannot take that meaning away from this phrase.
Then, to complete the matter, He declares that His people are in His hand and challenges all His enemies to snatch them from it. Surely this is impossible even for the devil of hell. We are safe, since we are in the hand of an Almighty Savior.
It is for us to cast aside carnal fear as well as carnal confidence, and rest quietly in the palm of the Redeemer’s hand.
Source: The Cheque Book of the Bank of Faith. Translation by Allan Roman.
http://www.spurgeon.com.mx/chequera/meditames/junio.pdf