Walk through Amos, verse by verse, with the great Bible Commentaries of Matthew Henry (1662 - 1714) & Adam Clarke (1760 - 1832)
{Wherefore, thou Israel, I shall do these things to thee; but after that I shall do to thee these things, Israel, be made ready into against-coming of thy God. }Wycliffe's Bible
Prepare to meet thy God, O Israel - This is a military phrase, and is to be understood as a challenge to come out to battle.
4:12
Therefore thus will I do unto thee, O Israel: and because I will do this unto thee, prepare to meet thy God, O Israel.
KJV
Prepare to meet thy God, O Israel - This is a military phrase, and is to be understood as a challenge to come out to battle.