Section 21. The tender may be made before the expiration of the three years limited for redemption, and before or after entry for breach of condition, and before a sale pursuant to a power contained in the mortgage; but if the mortgagee or person claiming or holding under him does not accept the tender and discharge the mortgage, the tender shall not prevent the foreclosure unless, within one year after the tender, the mortgagor or person claiming or holding under him commences suit for redemption and when he commences suit pays to the clerk of the court the amount tendered for the use of the party entitled thereto.