ISB ~ Galatians 4 v10

days … months … seasons … years:Refers to the liturgical calendar of Israel, which was regulated by the cycles of the sun and moon (Gen 1:14). Apparently the Judaizers persuaded some of the Galatians to begin celebrating the weekly (Sabbath, Ex 20:8-11), monthly (New Moon, Num 28:11-15), seasonal (Passover, Pentecost, etc., Deut 16:1-17), and yearly (New Years, see note on Lev 23:24) festivals of the Old Covenant (Col 2:16).