On this day we celebrate the Immaculate Conception–of Mary, not Jesus, even though our Gospel concerns the immediate conception of Jesus. But the Immaculate Conception of Mary is a logically necessary preparation for the conception of Jesus in his humanity–she must not be damaged by sin in any way if she is to agree to the conception of Jesus. Since she does agree to become the mother of this Child, we know she is untouched, undamaged, by the plague of original sin all other human beings from the first have passed on generation by generation.
It also follows from this that her question to the angel “How can (more literally, “how will”) this be, since I have no relations with a man?” is not a sinful one, but one of simple, genuine puzzlement. The angel points out that “Nothing is impossible for God!”
Yes, sexual intercourse between man and woman is necessary for conception, but God’s abilities are larger than the systems he sets in place. He can, and has, made exceptions. He has, according to Scripture, already created two human beings, Adam and Eve, without any male/female interaction at all! There he used mud to make Adam and material from Adam alone to make Eve. And he will go on to handle the birth of John the Baptist, even though his mother is past the normal age for conceiving a child. (As he had done once before with the conception of Isaac by Abraham and Sarah.) God makes “nature’s laws” but nature’s laws are also subject to their Creator.
One other happy note: think you are a poor excuse for a Christian? Remember: “Nothing is impossible for God!” Ask to become a better believer/actor in faith! Our laziness and stupidity are not impossible for God to change. Ask!