God knows the limitations of our human nature very well - after all, he created it. We can only focus our attention - really focus it - on one or two things at a time; we can't keep everything in mind all at once. But on the other hand, we can't focus our attention on the same thing all the time either; we need variety, otherwise we become depressed.
These limitations of our human nature are one reason God inspired the Church to divide the year into liturgical seasons.
The mystery of our salvation includes the whole Bible, the whole life of Christ, and the whole history of the Church.
But we can't possibly keep all those things in mind all the time.
So we focus on different aspects of them at different times of the year (which has the added benefit of giving variety to our spiritual lives): in Lent we focus on the reality of sin and mercy and the need for repentance; during Easter we focus on the power of God and the Resurrection; during Ordinary Time we focus on the everyday life and teachings of Christ and the wisdom they impart for our everyday lives; and now, during Advent, we focus on God's faithfulness.
St Paul puts it briefly in today's Second Reading: "God is faithful." God didn't abandon the human race after original sin. He promised to send a Savior, and he fulfilled his promise on the very first Christmas.
And God has also promised that this Savior, Jesus Christ, will come again to bring our earthly exile to its completion, just as in Old Testament times God brought his Chosen People out of their exile in Babylon, as today's First Reading reminded us.
God is faithful; he will fulfill his promises - that's one of the key themes for Advent.
In today's First Reading, Isaiah says twice, "Lord, you are our Father." By reminding us today that God always fulfills his promises, the Church wants to put that same prayer in our hearts.
God is our Father; he is always looking after us, protecting us, and loving us. And unlike earthly fathers, God's fatherly love has no limits, no imperfections, no blind spots.
Advent is meant to be a time when we renew our awareness of God's perfect Fatherhood in our lives, letting his love for us renew our spirits.
The best way to do that is to spend more time with God in prayer during this Advent season. But that will be impossible unless something else happens first.
Prayer is a funny thing: even though we usually don't see God with our physical eyes or hear him with our physical ears, when we turn our attention to him, he really is present, and we know it. As we become aware of this presence, we also, almost automatically, become aware of our own sinfulness, because God is truth, and his light shines into all the hidden corners of our heart.
If in those corners we have been hiding some un-repented and un-confessed sins, or harboring some sinful habits, as soon as we sincerely try to pray, they will come into view and distract us.
So, if we want to spend more time in prayer this Advent, filling our hearts with the Father's goodness and wisdom, the first thing we need to do is clean out those dark corners by taking a trip to the confessional.
Today, as we begin this sacred season, let's promise that we will let him clean up our dark corners, so that we can enjoy his presence as we prepare for the great commemoration of Christmas Day.