What is the meaning of “conceived by the Holy Spirit, born of the virgin Mary?”

Heidelberg Catechism

~His Incarnation

Question 35. What is the meaning of “conceived by the Holy Spirit, born of the virgin Mary?”

Answer. That the eternal Son of God, who is and continues true and eternal God,[1] took upon Himself the very nature of man, of the flesh and blood of the virgin Mary,[2] by the operation of the Holy Spirit;[3] so that He might also be the true seed of David,[4] like unto His brethren in all things,[5] except for sin.[6]

[1] Jn 1:1-4, 10:30-36; Rom 1:3-4, 9:5; Col 1:15-17; 1 Jn 5:20;
[2] Mt 1:18-23; Jn 1:14; Gal 4:4; Heb 2:14;
[3] Mt 1:18-20; Lk 1:35;
[4] 2 Sam 7:12-16; Ps 132:11; Mt 1:1; Lk 1:32; Rom 1:3;
[5] Php 2:7; Heb 2:17;
[6] Heb 4:15, 7:26-27