The mystery of piety is a sovereign act of God, in his mercy, of preparing to execute in future time the the only plan of salvation which included the death of his son Jesus Christ to benefit Jews and Gentiles alike. 1 Ti. 3:16.

      This is a very big mystery, difficult to understand for human logic. The plan established in the Divine Council for the redemption of man includes a series of extraordinary events that would be gradually fulfilled.

      It was necessary for the second person of the Divine Trinity (the Verb) to incarnate for the fulfillment of the successive prophetic events. Is. 7:14; Is. 9:6-7; Is. 53: 1-12; Lc. 1: 26-35; Mt. 1: 18-25.

Consider what I say, and the Lord give to you understanding in everything. 2 Ti. 2: 7.

And indisputably, great is the mystery of piety:
God was manifested in flesh,
Justified in the Spirit,
Seen from the angels,
Preached to the Gentiles,
Believed in the world,
Received up in glory. 1 Ti. 3:16.

14 Therefore the Lord himself will give you a sign: Behold, the virgin shall conceive, and bear a son, and shall call his name Immanuel. Is. 7: 14.

6 For a child is born to us, a son is given to us, and the principality on his shoulder; and his name will be called Wonderful, Counselor, Mighty God, Eternal Father, Prince of Peace.
7 The length of his empire and peace will have no limit, on the throne of David and on his kingdom, arranging and confirming it in judgment and in justice from now and forever. The zeal of Jehovah of armies will do this. Is. 9: 6-7.

4 He certainly took our diseases, and suffered our pains; and we felt him scourged, wounded by God and dejected.
5 But he was wounded for our transgressions, he was crushed for our sins; the punishment of our peace was upon him, and by his stripes we were healed.
6 All of us like sheep have gone astray, each one has turned aside in his way; but the Lord has laid on him the sin of us all.
Is. 53: 4-6.

30 Then the angel said to her: Mary, do not be afraid, because you have found favor with God.
31 And now, you will conceive in your womb, and bear a son, and you will call his name JESUS.
32 He will be great, and he will be called Son of the Most High; and the Lord God will give him the throne of David his father;
33 And he shall reign over the house of Jacob forever, and his kingdom shall have no end.
34 Then Mary said to the angel, How will this be? I do not know a man
35 The angel answered and said to him, The Holy Spirit will come upon you, and the power of the Most High will overshadow you; whereby also the Holy Being that will be born will be called Son of God. Lc. 1: 30-35.

18 The birth of Jesus Christ was like this: Mary being married to his mother with Joseph, before they met together, it was found that she had conceived of the Holy Spirit.
19 Joseph, her husband, because he was just, and did not want to make a name for her, wanted to leave her secretly.
20 And when he thought of this, behold, an angel of the Lord appeared to him in a dream and said to him, "Joseph, son of David, do not be afraid to receive Mary your wife, for what is begotten in her is from the Holy Spirit.
21 And she will bear a son, and you will call his name JESUS, [a] because he will save his people from their sins.
22 All this happened to fulfill what the Lord had said through the prophet, when he said:
23 Behold, a virgin shall conceive and bear a son,
And you will call his name Emmanuel, which translated is: God with us.
24 And Joseph waking from sleep, he did as the angel of the Lord commanded him, and he received his wife.
25 But he did not know her until she gave birth to her firstborn son; and he named him JESUS.
Mt. 1: 18-25.