EVER GET…= Do you ever get…?

SOMETHING IN YOUR HEAD= An idea (especially a persistent idea)

A CUT= A wound produced by something cutting.

BLADE= The part of a sharp weapon, tool, etc, that forms the cutting edge. A knife has a handle, which is the part where you hold it, and a blade made of metal; the blade has a sharp edge used for cutting.

BROUGHT TO YOUR KNEES= Kneeling down (because some power forced you or made you or inspired you to kneel down in praise or submission or in awe)

BUT YOU NEVER PRAYED= But you had never prayed before. To pray is to talk to God.

JESUS= /dʒi:zəs/ For Christians, Jesus is God. When God wanted to participate in human history (and of human nature) fully, he became a man, and that was Jesus. So in this song, if you are not a Christian, where they say "Jesus" simply read "God", but a God participating in your history, in your life, interacting with you.

IN DISGUISE= A disguise is some kind of costume that makes you look someone or something different; for example, in Carnival or Halloween you can disguise yourself as a ghost, a policeman or a vampire. If something is “in disguise”, it is not apparent, it looks something different so it is not easy to recognise. “A blessing in disguise” is a good thing that looks bad (for example you lost your job, but that was a blessing in disguise because then you could find a much better job). A friend in disguise would be someone who doesn’t look like he is your friend, but he is helping you, so he is your friend even if you don’t know it.
In this song they say JESUS IN DISGUISE. Here Jesus is the presence of God in our world, so there are many people, things and situations that are “Jesus in disguise”, because they reveal the presence of God but under a normal everyday appearance, so we often can’t recognise Him there.

JEHOVAH= /dʒɪhəʊvə/ Another name for God.
A few Christian branches (especially the Jehovah Witnesses) still believe that “Jehovah” is the name ancient Israelites used for God. The real name they used was lost in history because 500 years before Christ the pronunciation of the name of God was forbidden (to avoid blasphemy), and Hebrew spelling only used consonants, so all we have is YHWH. In medieval times some people reconstructed the original name as Jehovah (Latin J=Y and V=W), others as Yahweh. Today, most Christians do the same as the New Testament writers and simply substitute “the Lord” for the ancient YHWH, but some still use sometimes, or always, the name “Jehovah”.

BURDEN= Something that is emotionally difficult to bear.

A TEAR= /ə tɪə*/ A drop of the clear salty liquid that is secreted by the eye when we cry out of sadness, pain or emotion.

SCAR= A mark left on the skin when a wound heals. If you cut your finger you may later get a scar. In this song, “scar” only means “mark”, a sign left after something has happened. Maybe it is a reference of God opening the skies to come down to your life, so then the skies show a scar.

HOLD= To hold is to have something in your hand (or in your arms). To HOLD THE KEY means to have the solution to a problem or the answer to a mystery (because a key can open doors and boxes where secrets are hidden).

OPEN MY EYES= He's asking God to open his eyes (to make him understand) so that he can see God's presence in his life.

WIDE AS I CAN= “as wide as I can”. In comparisons like this, we can often drop the first AS, especially when we are using cliché (very common) comparisons:
- He is as tall as my father
- It was (as) hot as fire
AS WIDE AS I CAN means very very wide (till I can’t open my eyes any wider)

BLIND= If you are blind, you can’t see (also use metaphorically to show that you can’t understand).
BLIND AS I AM is not a comparative, it means “although I am blind” and with this meaning it is not possible to say "as...as" (as blind as I am). We can use this construction, which is the same as that for comparatives, to mean “although...”
- I continued walking, tired as I was, because I wanted to reach home before night = I continued walking although I was very tired, because I wanted  to...

So we have two constructions which apparently are the same, but in fact are different:

- wide as I can = as wide as I can (comparative, with omission of the first AS)

- blind as I am = although I am blind (concesive)