Hebrews 12:11

Now all chastening for the present indeed seemeth to be not joyous, but grievous; but afterward it yieldeth the peaceful fruit of righteousness to those who have been exercised thereby.

Matthew 10:37

He that loveth father or mother more than me, is not worthy of me; and he that loveth son or daughter more than me, is not worthy of me;

Treasury of Scripture Knowledge

Summary

And the thing was very grievous in Abraham's sight because of his son.

Bible References

Because

Matthew 10:37
He that loveth father or mother more than me, is not worthy of me; and he that loveth son or daughter more than me, is not worthy of me;
Hebrews 12:11
Now all chastening for the present indeed seemeth to be not joyous, but grievous; but afterward it yieldeth the peaceful fruit of righteousness to those who have been exercised thereby.