There is no one who can understand completely the mysteries of God. A portion of Romans speaks to that:

33 We cannot wrap our minds around God’s wisdom and knowledge! Its depths can never be measured! We cannot understand His judgments or explain the mysterious ways that He works! For,

34 Who can fathom the mind of the Lord?
Or who can claim to be His advisor?

35 Or,

Who can give to God in advance
so that God must pay him back?

36 For all that exists originates in Him, comes through Him, and is moving toward Him; so give Him the glory forever. Amen.  Romans 11;33-36 (THE VOICE)

Here we find the Apostle Paul addressing the Roman believers not to get too haughty about the wonderful gift of salvation that they have received. Paul has been stating the then present condition of the Jews, admitting that they rejected the Promise that came to be their deliverer.However, he advises them to understand two very important things about God; number one being that there is no one that can get into the mind of god or even be acceptable as His advisor; and secondly, there is nothing anyone can do to cause God to be their debtor.

God made everything and everyone. Everything comes through Him. Whatever comes to us comes to us by His great mercy. Therefore it was mercy that grafted the Gentiles into the olive branch, and it will be mercy that graft again the Jews back in. 

"For all have sinned and come short of the glory of God" )ROMANS 3:23), but "Oh the great mercies He extends to all people who will receive.

Maria