To trust in the promise of God is to trust in all the attributes of God which combine to fulfil it. It is God’s integrity that is at stake in promising us eternal life, and he sets a higher value on that than any cost he incurs in fulfilling the promise.
No one but God himself stands guard over his promise to ensure that he keeps it. A promise may seem a slender thread on which to hang so much weight, for it is a bare word with the substance still not visible, but that promise allows us to take hold of the heart of God, the God who cannot lie and who never disappoints or says more than he intends to do. By doing so we can enjoy the thing promised even before we possess it.