Ibn Ezra, on Isa 56:4

“For thus saith the Lord to the eunuchs, They that shall keep my sabbaths, and shall choose the things that please me, and shall hold fast my covenant:”

“That keep my sabbath, etc. The sabbath is mentioned, because it is a sign of the covenant between Him and those that keep it, on account of God having rested on it; he who keeps the Sabbath is, therefore, a worshipper of the Lord.”

Imported from an open dataset — not yet checked against the printed edition.