Gods Glory is manifested in Unconditional Sovereign Election and Reprobation. Election is a Matter of absolute Mercy Rom 9:11-15
11 (For the children being not yet born, neither having done any good or evil, that the purpose of God according to election might stand, not of works, but of him that calleth)
12 It was said unto her, The elder shall serve the younger.
13 As it is written, Jacob have I loved, but Esau have I hated.11
14 What shall we say then? Is there unrighteousness with God? God forbid.
15 For he saith to Moses, I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion.
God is not obligated to have mercy on any one of us, He would have been just to punish eternally everyone for their sins against Him.
However He purposed for His own Glory to have Mercy on only some, a remnant of mankind. Moses had asked God to show him His Glory, and the Lord answred Ex 33:18,19
18 And he said, I beseech thee, shew me thy glory.
19 And he said, I will make all my goodness pass before thee, and I will proclaim the name of the Lord before thee; and will be gracious to whom I will be gracious, and will shew mercy on whom I will shew mercy.
See that, God in responding to Moses said He will proclaim HIS NAME ! And in that proclamation we have the sacred words " and will be gracious to whom I will be gracious, and will shew mercy on whom I will shew mercy."
The Glory of the Lord is bound up in His Sovereign Prerogative to be merciful and gracious to whomever He pleases understanding that He can withhold the same to whomever He pleases.
Ps 115:3
3 But our God is in the heavens: he hath done whatsoever he hath pleased.