Albert Barnes Commentary Jeremiah 12:1

"Righteous art thou, O Jehovah, when I contend with thee; yet would I reason the cause with thee: wherefore doth the way of the wicked prosper? wherefore are all they at ease that deal very treacherously?" — Jeremiah 12:1 (ASV)

Yet let me talk ... - Rather, yet I will speak with you on a matter of justice. This sense is well given in the margin. The prophet acknowledges the general righteousness of God’s dealings, but cannot reconcile with it the prosperity of the conspirators of Anathoth. This difficulty was often present to the minds of the saints of the Old Testament (see Job 21:7 and following; Psalms 37; Psalms 73).

Happy - Rather, secure, tranquil.