وَارْ‌كَعِي مَعَ الرَّ‌اكِعِينَ (and bow down with those who bow) while giving an order to bow down, the imperative has been qualified with the words "with those who bow"- but no such qualification appears while giving an order of prostration. This apparently seems to hint that people generally do not observe due concern while making ruk a` (bowing). They tend to bend a little, then resume the standing position (as if in a hurry). This kind of رکوع ruku' (bowing) is closer to standing قیام (qiyam). As said earlier, it apparently seems to suggest that Allah Almighty, by mentioning the qualification 'those who bow', has given a model to be followed so that one's bowing in prayer could become similar to those who bow fully and perfectly as due.