10 “See that you do not despise one of these little ones. For I tell you that in heaven their angels always see the face of my Father who is in heaven.
Old Testament references:
So Jacob called the name of the place Peniel, saying, “For I have seen God face to face, and yet my life has been delivered.”
Thus the Lord used to speak to Moses face to face, as a man speaks to his friend. When Moses turned again into the camp, his assistant Joshua the son of Nun, a young man, would not depart from the tent.
and they will tell the inhabitants of this land. They have heard that you, O Lord, are in the midst of this people. For you, O Lord, are seen face to face, and your cloud stands over them and you go before them, in a pillar of cloud by day and in a pillar of fire by night.
The Lord spoke with you face to face at the mountain, out of the midst of the fire,
And there has not arisen a prophet since in Israel like Moses, whom the Lord knew face to face,
In the year that King Uzziah died I saw the Lord sitting upon a throne,
But what about the New Testament accounts?
No one has ever seen God; the only God, who is at the Father's side, he has made him known.
1 John 4:12
No one has ever seen God; if we love one another, God abides in us and his love is perfected in us.
1 Timothy 1:17
To the King of ages, immortal, invisible (can't be seen), the only God, be honor and glory forever and ever. Amen.
1 Timothy 6:16
who alone has immortality, who dwells in unapproachable light, whom no one has ever seen or can see. To him be honor and eternal dominion. Amen.
Here is some good commentary on John 1:18:
Overall, if God the Father is invisible and dwells in unapproachable light then we must understand that Christ is the physical manifestation of God the Father:
John 1:1 - In the beginning was the Word, and the Word was with God, and the Word was God.
John 1:14 - And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth.
Matthew 1:23 - “Behold, the virgin shall conceive and bear a son, and they shall call his name Immanuel” (which means, God with us).
We know that it is possible to look upon the face of God in Christ because He was on earth and many people saw Him. Could it be that the OT references to seeing God are actual pre-incarnate visions of Christ? I would think that this is entirely plausible as it would affirm both the diety and pre-existence of Christ and His oneness with the Father.
As for Matthew 18:10, the literal rendering of the word "see" comes from the GK word "hor·ah·o" which can mean to see with the eyes but it can also mean to see with ones mind or to perceive and understand the knowledge of something. Perhaps one of the best rendered understandings comes from Strong's Lexicon: "to see, i.e. become acquainted with by experience, to experience." This would give us an understanding that the angels mentioned (particular ones perhaps) are not necessarily staring at the face of God but rather that they are allowed to be in His immediate pressence. This would also give us a better inclination of the intimate relationship that God the Father has with those whom are under His divine protection (children in particular).
So are these contradictions? When we understand the whole picture of Christ I do not think so.