Bail

There is no need to get bail again on the only reason that the court issued summons for appearance. Summons meant for directing you to appear before the court in order to participate in the Court proceedings. 

If chargesheet is filed, then formally you have to take bail from the court.

Summons are issued by court and matter is before court then there must be chargesheet is filed in your case. Your lawyer is correct.

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Yes, court bail is  required.

unless and until your previous bail was cancelled, you have no need to take fresh bail.

summon was issued as because charge sheet has been filed and you need to attend the court for trial.

The procedure of obtaining court bail at the time of first appearance on summons before the court is mandatory in some states.  The procedure in some other states namely in Tamilnadu is different, once a person is  enlarged on bail, he need not have to obtain bail again during the first appearance as being practiced in the neighboring states.  Thus, if it is a procedure being followed in your state, your lawyer will be right in suggesting you to do that.  Confirm it from other lawyers too.