Some translations set poetry farther to the right than the rest of the text to show that it is poetry. The ULB does this with the poetry in verse 27, which is quoted from the Old Testament.
Sonship is a complex issue. Scholars have many views on Israel's sonship. Paul uses sonship to teach how being under the law differs from being free in Christ. Not all of Abraham's physical descendants inherited God's promises to him. Only his descendants through Isaac and Jacob inherited the promises. And God only adopts into his family those who follow Abraham spiritually through faith. They are children of God with an inheritance. Paul calls them "children of promise." (See: [[rc://en/tw/dict/bible/kt/inherit]], [[rc://en/tw/dict/bible/kt/promise]], [[rc://en/tw/dict/bible/kt/spirit]] and [[rc://en/tw/dict/bible/kt/faith]] and [[rc://en/tw/dict/bible/kt/adoption]])
"Abba" is an Aramaic word. In ancient Israel, people used it to informally refer to their fathers. Paul "transliterates" its sounds by writing them with Greek letters. (See: [[rc://en/ta/man/jit/translate-transliterate]])