Did God leave all mankind to perish in the estate of sin and misery?

Answer

God having out of his mere good pleasure, from all eternity, elected some to everlasting life (), did enter into a covenant of grace, to deliver them out of the estate of sin and misery, and to bring them into an estate of salvation by a Redeemer (; ).

Read the 3 proof texts (KJV)

Ephesians 1:4-5: ⁴According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love: ⁵Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will,
Romans 3:20-22: ²⁰Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law [is] the knowledge of sin. ²¹But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets; ²²Even the righteousness of God [which is] by faith of Jesus Christ unto all and upon all them that believe: for there is no difference:
Galatians 3:21-22: ²¹[Is] the law then against the promises of God? God forbid: for if there had been a law given which could have given life, verily righteousness should have been by the law. ²²But the scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe.