For Thomas Watson, a Puritan preacher of the 1600’s, the doctrine of eternal security for the genuine believer was more than a bit of knowledge to store away for a spiritually rainy day. It was a wonder at which he marveled, and a comfort upon which he rested.

Notice how he writes of God’s preserving power:

There is nothing that more troubles a child of God, than that he fears he shall never hold out. “These weak legs of mine,” he says, “will never carry me to Heaven!” But he is kept by the power of God! Once in Christ — forever in Christ. A believer may fall from some degrees of grace — but not from the state of grace.

How despairing is the Arminian doctrine of falling from grace! Today a saint — tomorrow a reprobate; today a Peter — tomorrow a Judas! This is  like boring a hole in a vessel — to make all the wine of his joy run out. Were the Arminian doctrine true, what comfort would it be — to have one’s name written in the book of life — if it might be blotted out again? But be assured, for your comfort, that grace — if it is true — though ever so weak, shall persevere. See whence it is, that believers persevere in holiness. It is to be ascribed solely to the power of God.

It is a wonder that any Christian perseveres, if you consider:

Corruption within. There is more sin than grace; yet grace is habitually predominant. Grace is like a spark in the sea — it is a wonder that it is not quenched! It is a wonder that sin does not destroy grace.

Temptations without. Satan envies us happiness, and he raises his militia, and stirs up persecution. He shoots his fiery darts of temptations — which are called darts for their swiftness, fiery for their terribleness. We are every day beset with devils! As it was a wonder that Daniel was kept alive in the midst of the roaring lions, so there are many roaring devils around us — and yet we are not torn in pieces! Now, whence is it, that we stand against these powerful temptations? We are kept by the power of God!

The world’s old snares — riches and pleasure. How many have been shipwrecked upon these golden rocks! “Demas has deserted me, because he loved this present world.” (2 Timothy 4:10)

What a wonder any persevere in holiness — that the earth does not choke the fire of all holy affections! Whence is this, but from the power of God? We are kept by His power.”

Source: Watson’s “A Body of Divinity”