Isaiah 1:15

And when ye spread forth your hands ,.... That is, in prayer, this being a prayer gesture: hence the Targum paraphrases it,

"and when the priests spread out their hands to pray for you.'

I will hide mine eyes from you ; will not look upon them, nor regard their prayer; see Lamentations 3:42 .

yea, when ye make many prayers ; as the Scribes and Pharisees did in Christ's time, and thought to be heard for their much speaking, like the Gentiles, Matthew 6:7 .

I will not hear ; so as to give an answer, or fulfil their requests: the reason follows,

your hands are full of blood ; of the prophets of the Lord, of Christ and his followers, whom they put to death.