If we sin and then repent and God then we think will always forgive us. This is so when it first happens, because our God is merciful, but if after sinning and repenting and being forgiven by God, we go back and repeat the thinking, "Well God forgave me the first time, I can go ahead and sin and He will forgive again."
Yes, God is merciful and He may accept our repentance a second time and a third and more but is there not limit to God's mercy when we repeatedly sin knowingly expecting that God will always be merciful and forgive again and again and again? Yes, there is a limit but you and I do not know what that limit is for us. If we knowingly sin in this manner and then before are able to repent again natural death takes us, is that not an indication that God's limit has been reached for us?
Consider these verses in the OT:
"Because all those men which have seen my glory, and my miracles, which I did in Egypt and in the wilderness, and have tempted me now these ten times, and have not hearkened to my voice;
Surely they shall not see the land which I sware unto their fathers, neither shall any of them that provoked me see it:" Num 14:22-23
These ten times refers to the times that children of Israel murmured and complained to Moses, [and thereby effectively to God]. Each time punishment was rendered and the people turned around and walked the line again until the next time they had a complaint against God. In the verse cited we see that they had reached God's limit. The guilty ones would die in the wilderness within the 40 year period and never be allowed to enter the Promised Land.
People may argue that that is the OT, not now when we have a better Covenant with God. There are problems with this way of thinking.
For one thing, God, Himself, never changes:
"For I am the LORD, I change not;.. " Mal 3:6
"Every good gift and every perfect gift is from above, and cometh down from the Father of lights, with whom is no variableness, neither shadow of turning." James 1:17
A second thing is that God is not and never has been a respecter of persons:
"These things also belong to the wise. It is not good to have respect of persons in judgment." Prov 24:23
"Then Peter opened his mouth, and said, Of a truth I perceive that God is no respecter of persons:" Acts 10:34
As to people having something better in the New Covenant, they do. They have, if they wish to acknowledge it and use it, the power of God to overcome their sinful ways. Jesus did not overcome our sinful ways. He overcame His [the world; John 16:33] and made it possible for us to overcome ours.
Because God has given us more than He gave those in the OT, He requires not less, but more, from us:
"But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more" Luke 12:48