What do "attain unto" and "apprehend" mean in the Bible?

Philippians 3:11 If by any means I might attain unto the resurrection of the dead. 12 Not as though I had already attained, either were already perfect: but I follow after, if that I may apprehend that for which also I am apprehended of Christ Jesus. 13 Brethren, I count not myself to have apprehended: but this one thing I do, forgetting those things which are behind, and reaching forth unto those things which are before,

Attain unto, in this context, means to understand, to wrap my mind around.

Psalm 139:6 Such knowledge is too wonderful for me; it is high, I cannot attain unto it.

Proverbs 1:5 A wise man will hear, and will increase learning; and a man of understanding shall attain unto wise counsels:

To apprehend also means to conceive by the mind according to Dr. Samuel Johnson's dictionary from the 1700's. Modern dictionaries will give a meaning as to understand something.

In this context it would be to know Christ as Christ knows him. So, in my mind I might say that these verses tell me that if by any means I might understand the resurrection of the dead, not that I understand it now, or am complete in my knowledge, but I follow after that I might understand and know Christ like he knows and understands me. Just don't change the words or you'll ruin the cross references for perfect and attain unto.