What assurance have we that God will doe so great things for naughty ones?

Answer

God hath given assurance of this by giving us his own Son; and making him our Surety; and by making a new Covenant, and by confirming it by his Sons death for us; and by raising him from death, to be a Prince and a Saviour, to give repentance and Pardon to Israel, to serve him all our dayes (; ; ; ; ; ; ).

Read the 7 proof texts (KJV)

Romans 8:31-33: ³¹What shall we then say to these things? If God be for us, who can be against us? ³²He that spared not his own Son, but delivered him up for us all, how shall he not with him also freely give us all things? ³³Who shall lay any thing to the charge of God’s elect? It is God that justifieth.
Hebrews 7:22, 25: ²²By so much was Jesus made a surety of a better testament. ²⁵Wherefore he is able also to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them.
Hebrews 8:10: For this is the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people:
Galatians 3:13, 15: ¹³Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree: ¹⁵Brethren, I speak after the manner of men; Though it be but a man’s covenant, yet if it be confirmed, no man disannulleth, or addeth thereto.
1 Corinthians 11:25: After the same manner also [he took] the cup, when he had supped, saying, This cup is the new testament in my blood: this do ye, as oft as ye drink [it], in remembrance of me.
Acts 5:30-31: ³⁰The God of our fathers raised up Jesus, whom ye slew and hanged on a tree. ³¹Him hath God exalted with his right hand to be a Prince and a Saviour, for to give repentance to Israel, and forgiveness of sins.
Psalm 68:18: Thou hast ascended on high, thou hast led captivity captive: thou hast received gifts for men; yea, [for] the rebellious also, that the LORD God might dwell [among them].