Let us therefore come boldly unto the throne of grace, that we may obtain mercy, and find grace to help in time of need. – Hebrews 4:16
The mercy seat is a throne; though grace is there, it is still a throne. Grace does not displace sovereignty. Now, the attribute of sovereignty is very high and terrible; its light is like unto a jasper stone, most precious, and like unto a sapphire stone, or, as Ezekiel calls it, “the terrible crystal.” Thus saith the King, the Lord of hosts: “I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion.” “Who art thou, O man, that repliest against God? Shall the thing formed say to Him that formed it, Why hast Thou made me thus?” “Hath not the potter power over the clay to make of the same lump one vessel unto honour and another unto dishonour?” These are great and terrible words, and are not to be answered. He is a King, and He will do as He wills. None shall stay His hand, or say unto Him, What doest Thou? But, ah! lest any of you should be downcast by the thought of His sovereignty, I invite you to the text. It is a throne,-there is sovereignty; but to every soul that knows how to pray, to every soul that by faith comes to Jesus, the true mercy seat, divine sovereignty wears no dark and terrible aspect, but is full of love. It is a throne of grace; from which I gather that the sovereignty of God to a believer, to a pleader, to one who comes to God in Christ, is always exercised in pure grace. To you, to you who come to God in prayer, the sovereignty always runs thus: “I will have mercy on that sinner; though he deserves it not, though in him there is no merit, yet because I can do as I will with My own, I will bless him, I will make him My child, I will accept him; he shall be Mine in the day when I make up My jewels.” On the mercy seat God never executed sovereignty otherwise than in a way of grace. He reigns, but in this case grace reigns through righteousness unto eternal life by Jesus Christ our Lord.~ C.H. Spurgeon
https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/1024.cfm