There are many causes of mental impairment and The Bible describes symptoms we all recognise today. Exactly the same symptoms are described in "medical dictionaries" but oh boy, do they ever get it wrong as to the causes! Jesus, who made the stars and the whole world and everything in it including people with mental impairments and who knows all about the causes and who is just waiting for the prayer of faith so that He can heal them, understands that as Christians we are seen as crazy for loving Him.
ROMANS 8 . KJV . look up
26 Likewise the Spirit also helpeth our infirmities: for we know not what we should pray for as we ought: but the Spirit itself maketh intercession for us with groanings which cannot be uttered.
27 And he that searcheth the hearts knoweth what is the mind of the Spirit, because he maketh intercession for the saints according to the will of God.
28 And we know that all things work together for good to them that love God, to them who are the called according to his purpose.
29 For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
30 Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified.
It follows very easily then that whom He has not glorified has not been justified and thus has not been called. Not having been called results from not having been predestinated as is shown from non-conformity to the image of His Son. Therefore such a person God did not foreknow. It probably seems unfair to the unregenerate fool who denies God's word and substitutes whatever seems trendy on the day that God would only redeem some people but not others. But is it unfair that people deserving of everlasting torment, deserving FROM CONCEPTION, receive everlasting torment? Of course not!
Paul is very aware that God's elect, the ones who are delivered by an act of grace from endless torture for the sin of being conceived in a belly descended from Eve, have the wonderful gift of Salvation based on a promise. That this promise is not based on a lie and that he is preaching to us The Truth. He explains:
TITUS 1 . KJV . look up
1 Paul, a servant of God, and an apostle of Jesus Christ, according to the faith of God's elect, and the acknowledging of the truth which is after godliness;
2 In hope of eternal life, which God, that cannot lie, promised before the world began;
3 But hath in due times manifested his word through preaching, which is committed unto me according to the commandment of God our Saviour.
When God is for us, who can be against us?
Praise Jesus!