Here’s St. Bernard on the fullness of time:
“When the fulness of time came, there came too the fulness of the Godhead. He came in the flesh, so that at least he might make himself manifest to our earthly minds, so that when this humanity of his appeared, his kindness might also be acknowledged. Where the humanity of God appears, his kindness can no longer be hidden. In what way, indeed, could he have better commended his kindness than by assuming my flesh? My flesh, that is, not Adam’s, as it was before the fall.
“What greater proof could he have given of his mercy than by taking upon himself that very thing which needed mercy? Where is there such perfect loving-kindness as in the fact that for our sake the Word of God became perishable like the grass? Lord, what is man, that you make much of him or pay him any heed?
“Let us infer from this how much God cares for us. Let us know from this what God thinks of us, what he feels about us. Do not ask about your own sufferings; but about what God suffered. Learn from what he was made for you, how much he makes of you, so that his kindness may show itself to you from his humanity.
“The lesser he has made himself in his humanity, the greater has he shown himself in kindness. The more he humbles himself on my account, the more powerfully he engages my love. The kindness and humanity of God our Saviour appeared says St Paul. The humanity of God shows the greatness of his kindness, and he who added humanity to the name of God gave great proof of this kindness.”