In the minds of many these terms are interchangeable, but that is erroneous. Love is "reciprocal," or giving and receiving mutually, a to and fro operation: but grace is "unilateral" or one-sided. "We love Him because He first loved us" (1 John 4:19). God is love: that is a terse description of what God is. It would be incongruous to say, "God is grace." He is gracious or the God of grace, the giving God; but grace is not reciprocal, it only acts in one way, i.e., between God and man. God was manifested as the God of grace in giving His Son; but obviously grace cannot flow in return from man to God. But there is a further transmission of grace from the individual receiving to those around. So even epistle closes with the invocation that grace (that of the Lord Jesus Christ) may be with every local company of Christians. Originally that grace flows from God and after permeating the individual Christians overflows and forms the medium between them, but it does not stop there. It goes outside the Christian sphere to the strangers around! What proceeds out of the Christian's mouth should be good to the use of edifying that it may minister grace unto the hearer; that will reach further than the Christians. (Eph. 4:29).
The love which subsisted reciprocally between the Father and the Son before time, continued while the Son was here and is the same now in His place of exaltation. But grace could not be, until there was the need of man in consequence of the entrance of sin. "Where sin abounded, grace did much more abound." So that the reign of sin unto death is superseded by the reign of grace unto eternal life, on account of righteousness having been accomplished by Jesus Christ our Lord (Rom. 5:20, 21). The reign of grace has the object of bringing man into the enjoyment of the love of God. The reign of grace will terminate when righteousness becomes dominant in the world to come. Grace removes every hindrance to that end and subjugates refractory elements to the authority of the Lord. Who could have predicted the reduction of Saul of Tarsus from the state of an overbearing Pharisee to that of a humble worker in God's service? Grace will then have served its purpose, but love will continue. God will ultimately rest in His love. He will rejoice over a redeemed creation which He will have brought to rest in His love. But there is a present aspect for the Christian. The appropriation of that love is hindered by fear or apprehension! "Perfect love casts out fear, because fear has torment." "Herein is love with us made perfect (or complete) in order that we may have boldness (confidence) in (or in view of) the day of judgment, because as He is so are we in this world" (1 John 4:17, 18). "As he is" implies being in the atmosphere of love which envelops the Father and the Son. It is not "so shall we be" but "so we are" in this world. If we realise that we are loved as Christ is loved, can we have any apprehension as to the present or the future?