John 8:40

But now ye seek to kill me, a man that hath told you the truth, which I have heard of God: this did not Abraham.

Spoken to unbelieving Jews who claimed Abraham as father, Jesus declared himself a man telling the truth he heard and received from God, whom they sought to kill for that truth, which Abraham never did.
Physical descent from Abraham by name and lineage has no virtue in itself and cannot guarantee favor or salvation, since true sonship is decided only by doing his works in obedience, faith, and spiritual harmony with him.
Seeking to kill one who speaks truth given from God proves the plotters have no spiritual connection with Abraham and are not his true children.
That rejection unmasked their works as aligned with the devil, a liar and murderer, rather than with God, dividing people into children of light who obey the truth and children of darkness who reject it.
The same test still exposes all who call God their Father yet hate the word of truth, for the hatred that sought to kill Christ continues and would crucify him again if it dared and had the power.

Context and Plain Meaning

The saying belongs to Jesus' teaching in the temple in which He presented Himself as the light of the world and promised that those who follow Him leave darkness for the light of life. It was spoken to unbelieving Jews who, when His words cut to the citadel of the soul, angrily claimed Abraham as their father. In it He identified Himself as a man telling the truth He had heard and received from God. His hearers sought to kill Him for telling that truth. This Abraham never did, and their murderous intent stood in direct contrast to Abraham's conduct and example.

True Children of Abraham

Being called Abraham's offspring by blood and bearing his name has no worth in itself and carries no virtue, and it does not make anyone his spiritual child nor secure divine favor and salvation. Those who angrily claimed Abraham as father while plotting to kill the One who told them God's truth were acting unlike Abraham, and their unbelief and rejection of truth shown in their deeds set them against him who obeyed God and was counted righteous. Ancestry and profession cannot take the place of a life reflecting his faith and conduct, for worthiness of his name would have been shown by following his righteous example.

A claim to be Abraham's children can be established only by doing the works of Abraham. True sonship is decided not by fleshly descent but by a life of obedience to God, possessing the same spirit, sharing his faith, and being spiritually in harmony with him. Those who obey God's voice are his true children, while seeking to kill Him who speaks truth heard and received from God proves the plotters have no spiritual connection with Abraham and are not his children, because Abraham did not do such a deed. If they truly followed Abraham's example they would not seek to kill the speaker of truth given by God, and their murderous plan contradicts their claim.

Moral and spiritual connection supersedes all natural connection, so only those spiritually in harmony with Abraham are reckoned of true descent. Even a beggar despised by men as inferior and low in human eyes can be one whom Abraham welcomes as a close friend and takes into the very heart of friendship. By the same principle apostolic succession is decided, resting not on transmission of ecclesiastical authority but on spiritual relationship shown by a life actuated by the apostles' spirit and by believing and teaching the truth they taught.

Rejection of Truth Unmasked

The refusal to believe exposed opposition to truth, for His words offended because truth uncovered error and condemned teaching and practice, and rather than admit error they preferred not to hear it. That rejection showed their works aligned them with the devil, a liar and murderer, rather than with God. Their murderous hatred was urged on by the accusing spirit of Satan, whose advocates they were, and being under his training they treated God's messenger as he directed, hating message and messenger because truth disturbed their deceptive practices.

The verse divides people into children of light who obey the truth and children of darkness who reject the truth and do the deeds of their true father. The same test exposes all today who call God their Father yet hate with intense hatred the word of truth. The Jewish nation at His first advent sought to kill Jesus because He told the truth heard from God, and that same hatred of truth continues, so wicked rulers and apostate churches converted to the world have no more desire for Christ today than the Jews had then and would do as the Jews did and crucify Him if they dared and had the power because He tells the truth. The same hostility to truth would lead rulers and religious leaders in this age to want to crucify Him if they had the power.